Commitments and Contingencies The following table presents the Bank's various off-balance sheet commitments which are described in detail below. (in thousands) June 30, 2019 December 31, 2018 Notional amount Expiration Date Within One Year Expiration Date After One Year Total Total Standby letters of credit outstanding (1) (2) $ 17,072,477 $  $ 17,072,477 $ 20,250,625 Commitments to fund additional advances and BOB loans 49,452  49,452 10,987 Commitments to purchase mortgage loans 53,287  53,287 17,391 Unsettled consolidated obligation bonds, at par 147,000  147,000 196,500 Unsettled consolidated obligation discount notes, at par 228,735  228,735 583,940 Notes : (1) Excludes approved requests to issue future standby letters of credit of $93.4 million and $75.3 million at June 30, 2019 and December 31, 2018 , respectively. (2) Letters of credit in the amount of $4.2 billion and $3.9 billion at June 30, 2019 and December 31, 2018 , respectively, have annual renewal language that, as long as both parties agree, permit the letter of credit to be renewed for an additional year with a maximum renewal period of approximately 5 years . Commitments to Extend Credit on Standby Letters of Credit, Additional Advances and BOB Loans. Standby letters of credit are issued on behalf of members for a fee. A standby letter of credit is a financing arrangement between the Bank and its member. If the Bank is required to make payment for a beneficiarys draw, these amounts are withdrawn from the members Demand Deposit Account (DDA). Any remaining amounts not covered by the withdrawal from the members DDA are converted into a collateralized overnight advance. Unearned fees related to standby letters of credit are recorded in other liabilities and had a balance of $3.0 million and $3.9 million as of June 30, 2019 and December 31, 2018 , respectively. The Bank monitors the creditworthiness of its standby letters of credit based on an evaluation of the member. The Bank has established parameters for the review, assessment, monitoring and measurement of credit risk related to these standby letters of credit. Based on managements credit analyses, collateral requirements, and adherence to the requirements set forth in Bank policy and Finance Agency regulations, the Bank has not recorded any additional liability on these commitments and standby letters of credit. Refer to Note 8 - Allowance for Credit Losses in this Form 10-Q. Excluding BOB, commitments and standby letters of credit are collateralized at the time of issuance. The Bank records a liability with respect to BOB commitments, which is reflected in Other liabilities on the Statement of Condition. The Bank does not have any legally binding or unconditional unused lines of credit for advances at June 30, 2019 or December 31, 2018 . However, within the Bank's Open RepoPlus advance product, there were conditional lines of credit outstanding of $9.9 billion and $8.7 billion at June 30, 2019 and December 31, 2018 , respectively. Commitments to Fund or Purchase Mortgage Loans. The Bank may enter into commitments that unconditionally obligate the Bank to purchase mortgage loans under the MPF Program. These delivery commitments are generally for periods not to exceed 60 days . Such commitments are recorded as derivatives. Pledged Collateral. The Bank may pledge cash and securities, as collateral, related to derivatives. Refer to Note 9 - Derivatives and Hedging Activities in this Form 10-Q for additional information about the Bank's pledged collateral and other credit-risk-related contingent features. Legal Proceedings. The Bank is subject to legal proceedings arising in the normal course of business. The Bank would record an accrual for a loss contingency when it is probable that a loss has been incurred and the amount can be reasonably estimated. After consultation with legal counsel, management does not anticipate that the ultimate liability, if any, arising out of these matters will have a material effect on the Bank's financial condition, results of operations or cash flows. Notes 6, 9, 10, 11, and 12 also discuss other commitments and contingencies.