v2.4.0.6
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Balance, beginning of period $ 17 $ 30 $ 38
Included in net income:      
Included in operating revenues 8 [1] 5 [1] 7 [1]
Included in fuel and purchased energy expense 0 [2] 0 [2] 0 [2]
Included in OCI 0 2 2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 3 0 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issues (1) 0 0
Purchases, issuances and settlements:      
Settlements (11) (18) (20)
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount 0 0 0
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount 0 0 0
Transfers into level 3 0 [3],[4] (2) [3],[4] 0 [3],[4]
Transfers out of level 3 0 [4],[5] 0 [4],[5] 3
Balance, end of period 16 17 30
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Change in Unrealized Gain (Loss) Held At Period End 8 [2] 5 [2] 7 [2]
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) [Abstract]      
Cash Equivalents Included In Cash And Cash Equivalents, Fair Value Disclosure 1,274 1,249  
Cash Equivalents Included In Restricted Cash, Fair Value Disclosure $ 228 $ 166  
[1] For power contracts and Heat Rate swaps and options, included on our Consolidated Statements of Operations.
[2] For natural gas contracts, swaps and options, included on our Consolidated Statements of Operations.
[3] There were no significant transfers into level 3 for the years ended December 31, 2012 and 2010. We had $2 million in losses transferred out of level 2 into level 3 for the year ended December 31, 2011 due to changes in market liquidity in various power and natural gas markets.
[4] We transfer amounts among levels of the fair value hierarchy as of the end of each period. There were no significant transfers into/out of level 1 during the years ended December 31, 2012, 2011 and 2010.
[5] We had no significant transfers out of level 3 for the years ended December 31, 2012 and 2011. There were $3 million in losses transferred out of level 3 into level 2 for the year ended December 31, 2010 due to changes in market liquidity in various power markets.