Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018		Dec. 31, 2018	Dec. 31, 2017
Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ 433			$ 102
Net unrealized investment gains	334	$ 0
Other Comprehensive Income	331	344
Foreign currency translation adjustments	1	1
Adoption of new accounting standard	178	(13)	[1]
Net cash flow hedges	(4)	343
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 months, net	18
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Comprehensive Income Loss [Line Items]
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax	0	464
Cumulative Effect of New Accounting Principle in Period of Adoption, before tax	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	(5)	(1)
Accumulated Other Comprehensive Income (Loss), Net of Tax	308	325		312	$ (15)
Adoption of new accounting standard	0	(3)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	344
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(4)	(1)
Net Unrealized Gains (Losses) Previously Impaired Securities [Member]
Comprehensive Income Loss [Line Items]
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax	410	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	(19)	0
Accumulated Other Comprehensive Income (Loss), Net of Tax	431	0		97	0
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	348	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(14)	0
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(157)	(128)		(158)	(129)
Other Comprehensive Income	1	1
Foreign Currency and Derivative Gain (Loss) [Member]
Comprehensive Income Loss [Line Items]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss), before Reclassification and Tax	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax	0	0
Pension and OPEB Plan [Member]
Comprehensive Income Loss [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption, before tax	0	0
Accumulated Other Comprehensive Income (Loss), Net of Tax	(149)	(25)		(149)	(21)
Other Comprehensive Income	0	0
Adoption of new accounting standard	0	(4)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	0	0
Accumulated Other Comprehensive Loss
Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	433	172		$ 102	$ (165)
Accumulated Other Comprehensive Loss
Comprehensive Income Loss [Line Items]
Other Comprehensive Income	331	344
Adoption of new accounting standard	$ 0	$ (7)	[1]

[1] (3)Reflects the adoption of ASU 2014-09, Revenue from Contracts with Customers, which resulted in a reduction to retained earnings of $13 million and the adoption of ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which resulted in a reduction to accumulated other comprehensive income and an increase to retained earnings of $7 million.