8. COMMITMENTS AND CONTINGENCIES Leases At December 31, 2011, our future minimum lease payments under operating leases (with initial or remaining noncancelable lease terms in excess of one year) were as follows: Year Amount 2012 $ 12 2013 5 2014 5 2015 3 2016 3 Thereafter 1 Total future minimum lease payments $ 29 Rent charged to operation and maintenance expense totaled $15 million for each of the years ended December 31, 2011 and 2010 and $11 million for the year ended December 31, 2009. Capital Expenditures We and Texas Holdings agreed to the terms of a stipulation with major interested parties that was approved by the PUCT in 2008 as discussed in Note 3. As one of the provisions of this stipulation, we committed to minimum capital spending of $3.6 billion over the five-year period ending December 31, 2012, subject to certain defined conditions. At December 31, 2011, approximately 94% of this total had been spent. These expenditures do not include the CREZ facilities. Efficiency Spending We are required to annually invest in programs designed to improve customer electricity demand efficiencies to satisfy ongoing regulatory requirements. The 2012 requirement (excluding the amount in excess of regulatory requirements) is approximately $50 million. Guarantees We have entered into contracts that contain guarantees to unaffiliated parties that could require performance or payment under certain conditions as discussed below. We are the lessee under various operating leases that obligate us to guarantee the residual values of the leased assets. At December 31, 2011, both the aggregate maximum amount of residual values guaranteed and the estimated residual recoveries totaled approximately $7 million. These leased assets consist primarily of vehicles used in distribution activities. The average life of the residual value guarantees under the lease portfolio is approximately 1.5 years. In June 2010, for the purpose of obtaining greater access to materials, we guaranteed the repayment of borrowings under a nonaffiliated