v3.8.0.1
Derivative Instruments (Textuals) (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Mar. 31, 2017
Dec. 31, 2016
Derivatives, Fair Value [Line Items]            
Current Derivatives Assets, net of Collateral $ (4)   $ (4)     $ (29)
Long-Term Derivative Assets, net of Collateral (8)   (8)     (3)
Current Derivative Liabilities, net of Collateral 43   43     19
Derivative, Collateral, Right to Reclaim Cash 115   115     262
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax 1 $ 0 $ 3 $ 0    
Summary of Derivative Instruments [Abstract]            
Maximum length of time hedging using interest rate derivative instruments     8 years      
Derivative, Net Liability Position, Aggregate Fair Value 17   $ 17      
Collateral Already Posted, Aggregate Fair Value 1   1      
Additional Collateral, Aggregate Fair Value 1   1      
Cash Flow Hedge (Gain) Loss to be Reclassified within Twelve Months     35      
Long-term Derivative Liabilities, net of Collateral 51   51     85
Parent [Member]            
Derivatives, Fair Value [Line Items]            
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax 101   101     90
Noncontrolling Interest [Member]            
Derivatives, Fair Value [Line Items]            
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax $ 7   $ 7     $ 8
2021 through 2022 [Member] | Interest Rate Hedging Instruments            
Derivatives, Fair Value [Line Items]            
Derivative, Amount of Hedged Item         $ 500  
2020 [Member] | Interest Rate Hedging Instruments            
Derivatives, Fair Value [Line Items]            
Derivative, Amount of Hedged Item         2,500  
2018 through 2020 [Member] | Interest Rate Hedging Instruments            
Derivatives, Fair Value [Line Items]            
Derivative, Amount of Hedged Item         1,000  
2021 [Member] | Interest Rate Hedging Instruments            
Derivatives, Fair Value [Line Items]            
Derivative, Amount of Hedged Item         $ 1,250