Derivative Instruments (Textuals) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Current Derivatives Assets, net of Collateral	$ (21)		$ (8)
Long-Term Derivative Assets, net of Collateral	(3)		(2)
Current Derivative Liabilities, net of Collateral	164		52
Derivative, Collateral, Right to Reclaim Cash	206		155
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax	$ 11	$ 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	$ 525
Collateral Already Posted, Aggregate Fair Value	439
Additional Collateral, Aggregate Fair Value	11
Cash Flow Hedge (Gain) Loss to be Reclassified within Twelve Months	1
Long-term Derivative Liabilities, net of Collateral	79		20
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	30		72
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		$ 6