Derivative Instruments (Textuals) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative, Collateral, Right to Reclaim Cash	$ 244	$ 155
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	$ 1	1
Maximum length of time hedging using interest rate derivative instruments	7 years
Derivative, Net Liability Position, Aggregate Fair Value	$ 229
Collateral Already Posted, Aggregate Fair Value	178
Additional Collateral, Aggregate Fair Value	3
Other Comprehensive Income Loss Derivatives Qualifying As Hedges Tax	5	6	$ 1
(Gain) Loss on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring, Net	1	0	3
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	(11)
Collateral Offset in Current Derivatives Assets	(58)	(8)
Collateral Offset in Long-Term Derivative Assets	(8)	(2)
Collateral Offset in Current Derivative Liabilities	49	52
Collateral Offset in Long-term Derivative Liabilities	64	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	(34)	(72)	(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	$ (3)	$ (6)	$ (8)