v3.6.0.2
Derivative Instruments (Details 3) (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]                      
Gain (Loss) on Sale of Derivatives [1],[2]                 $ 235 $ 450 $ 110
Unrealized Gain (Loss) on Derivatives [3]                 1 (110) 353
Derivatives contracts included in operating revenues $ 1,582 $ 2,355 $ 1,164 $ 1,615 $ 1,436 $ 1,948 $ 1,442 $ 1,646 6,716 6,472 8,030
Derivatives contracts included in fuel and purchased energy                 4,187 3,767 4,892
Interest expense                 631 628 645
Gain (Loss) on Derivative Instruments, Net, Pretax [4]                 236 340 463
Energy Related Derivative [Member]                      
Derivative Instruments, Gain (Loss) [Line Items]                      
Gain (Loss) on Sale of Derivatives [1],[2]                 235 450 110
Unrealized Gain (Loss) on Derivatives [3]                 (1) (113) 342
Interest Rate Contract [Member]                      
Derivative Instruments, Gain (Loss) [Line Items]                      
Unrealized Gain (Loss) on Derivatives [3]                 2 3 11
Interest expense [4],[5]                 2 3 11
Power [Member]                      
Derivative Instruments, Gain (Loss) [Line Items]                      
Derivatives contracts included in operating revenues [4],[6],[7]                 109 528 384
Natural Gas [Member]                      
Derivative Instruments, Gain (Loss) [Line Items]                      
Derivatives contracts included in fuel and purchased energy [4],[6],[7]                 $ 125 $ (191) $ 68
[1] Does not include the realized value associated with derivative instruments that settle through physical delivery.
[2] Includes amortization of acquisition date fair value of financial derivative activity related to the acquisition of Champion Energy and Calpine Solutions, formerly Noble Solutions.
[3] In addition to changes in market value on derivatives not designated as hedges, changes in mark-to-market gain (loss) also includes hedge ineffectiveness and adjustments to reflect changes in credit default risk exposure.
[4] In addition to changes in market value on derivatives not designated as hedges, changes in mark-to-market gain (loss) also includes adjustments to reflect changes in credit default risk exposure.
[5] In addition to changes in market value on interest rate hedging instruments not designated as hedges, changes in mark-to-market gain (loss) also includes hedge ineffectiveness.
[6] Does not include the realized value associated with derivative instruments that settle through physical delivery.
[7] Includes amortization of acquisition date fair value of financial derivative activity related to the acquisition of Champion Energy and Calpine Solutions, formerly Noble Solutions.