v3.19.2
Derivative Instruments (Textuals) (Details) - USD ($)
 3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Derivatives, Fair Value [Line Items]          
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net   $ 1,000,000   $ 1,000,000  
Current Derivatives Assets, net of Collateral $ (27,000,000)   $ (27,000,000)   $ (58,000,000)
Long-Term Derivative Assets, net of Collateral (3,000,000)   (3,000,000)   (8,000,000)
Current Derivative Liabilities, net of Collateral 72,000,000   72,000,000   49,000,000
Long-term Derivative Liabilities, net of Collateral 104,000,000   104,000,000   64,000,000
Derivative, Collateral, Right to Reclaim Cash 142,000,000   142,000,000   244,000,000
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax 1,000,000 (7,000,000) $ (1,000,000) (4,000,000)  
Summary of Derivative Instruments [Abstract]          
Maximum length of time hedging using interest rate derivative instruments     6 years    
Derivative, Net Liability Position, Aggregate Fair Value 230,000,000   $ 230,000,000    
Collateral Already Posted, Aggregate Fair Value 171,000,000   171,000,000    
Additional Collateral, Aggregate Fair Value 5,000,000   5,000,000    
Gain (Loss) on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring, Net 0 $ 0 1,000,000 $ 0  
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months     20,000,000    
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 89,000,000   89,000,000   34,000,000
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 $ 4,000,000   $ 4,000,000   $ 3,000,000