Revenue Recognition Revenue from Contracts with Customers On January 1, 2018, the Company adopted the guidance in ASC 606, Revenue from Contracts with Customers, or Topic 606, using the modified retrospective method applied to contracts which were not completed as of the adoption date, with no adjustment required to the financial statements upon adoption. Following the adoption of the new standard, the Companys revenue recognition of its contracts with customers remains materially consistent with its historical practice. The comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods. The Company's policies with respect to its various revenue streams are detailed below. In general, the Company applies the invoicing practical expedient to recognize revenue for the revenue streams detailed below, except in circumstances where the invoiced amount does not represent the value transferred to the customer. Thermal Revenues Steam and chilled water revenue is recognized as the Company transfers the product to the customer, based on customer usage as determined by meter readings taken at month-end. Some locations read customer meters throughout the month, and recognize estimated revenue for the period between meter read date and month-end. For thermal contracts, the Companys performance obligation to deliver steam and chilled water is satisfied over time and revenue is recognized based on the invoiced amount. The Thermal Business subsidiaries collect and remit state and local taxes associated with sales to their customers, as required by governmental authorities. These taxes are presented on a net basis in the income statement. As contracts for steam and chilled water are long-term contracts, the Company has performance obligations under these contracts that have not yet been satisfied. These performance obligations have transaction prices that are both fixed and variable, and that vary based on the contract duration, customer type, inception date and other contract-specific factors. For the fixed price contracts, the Company cannot accurately estimate the amount of its unsatisfied performance obligations as it will vary based on customer usage, which will depend on factors such as weather and customer activity. Power Purchase Agreements, or PPAs The majority of the Companys revenues are obtained through PPAs or other contractual agreements. Energy, capacity and where applicable, renewable attributes, from the majority of the Companys renewable energy assets and certain conventional energy plants is sold through long-term PPAs and tolling agreements to a single counterparty, which is often a utility or commercial customer. The majority of these PPAs are accounted for as leases. ASC 840 requires the minimum lease payments received to be amortized over the term of the lease and contingent rentals are recorded when the achievement of the contingency becomes probable. Judgment is required by management in determining the economic life of each generating facility, in evaluating whether certain lease provisions constitute minimum payments or represent contingent rent and other factors in determining whether a contract contains a lease and whether the lease is an operating lease or capital lease. Renewable Energy Credits, or RECs As stated above, renewable energy credits, or RECs, are usually sold through long-term PPAs. Revenue from the sale of self-generated RECs is recognized when the related energy is generated and simultaneously delivered even in cases where there is a certification lag as it has been deemed to be perfunctory. In a bundled contract to sell energy, capacity and/or self-generated RECs, all performance obligations are deemed to be delivered at the same time and hence, timing of recognition of revenue for all performance obligations is the same and occurs over time. In such cases, it is often unnecessary to allocate transaction price to multiple performance obligations. Sale of Emission Allowances The Company records its bank of emission allowances as part of intangible assets. From time to time, management may authorize the transfer of emission allowances in excess of usage from the Company's emission bank to intangible assets held-for-sale for trading purposes. The Company records the sale of emission allowances on a net basis within operating revenue in the Company's consolidated statements of operations. Disaggregated Revenues The following tables represent the Companys disaggregation of revenue from contracts with customers for the three and nine months ended September 30, 2018 , along with the reportable segment for each category: Three months ended September 30, 2018 (In millions) Conventional Generation Renewables Thermal Total Energy revenue (a) $ 2 $ 167 $ 50 $ 219 Capacity revenue (a) 86  4 90 Contract amortization (1 ) (15 ) (1 ) (17 ) Total operating revenue 87 152 53 292 Less: Lease revenue (88 ) (158 )  (246 ) Less: Contract amortization 1 15 1 17 Total revenue from contracts with customers $  $ 9 $ 54 $ 63 (a) The following amounts of energy and capacity revenue relate to leases and are accounted for under ASC 840: Conventional Generation Renewables Total Energy Revenue $ 2 $ 158 $ 160 Capacity Revenue 86  86 88 158 246 Nine months ended September 30, 2018 (In millions) Conventional Generation Renewables Thermal Total Energy revenue (b) $ 5 $ 473 $ 139 $ 617 Capacity revenue (b) 250  9 259 Contract amortization (4 ) (46 ) (2 ) (52 ) Total operating revenue 251 427 146 824 Less: Lease revenue (255 ) (438 ) (1 ) (694 ) Less: Contract amortization 4 46 2 52 Total revenue from contracts with customers $  $ 35 $ 147 $ 182 (b) The following amounts of energy and capacity revenue relate to leases and are accounted for under ASC 840: Conventional Generation Renewables Thermal Total Energy Revenue $ 5 $ 438 $ 1 $ 444 Capacity Revenue 250   250 255 438 1 694 Contract Amortization Assets and liabilities recognized from power sales agreements assumed through acquisitions related to the sale of electric capacity and energy in future periods for which the fair value has been determined to be significantly less (more) than market are amortized to revenue over the term of each underlying contract based on actual generation and/or contracted volumes or on a straight-line basis, where applicable. Contract Balances The following table reflects the contract assets and liabilities included on the Companys balance sheet as of September 30, 2018 : (In millions) September 30, 2018 Accounts receivable, net - Contracts with customers $ 35 Accounts receivable, net - Leases 106 Total accounts receivable, net $ 141