Accumulated Other Comprehensive Loss (Before and After Tax) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	$ 237	$ 13	$ (65)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	105	185	155
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax	132	(172)	(220)
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	(45)	20	26
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(13)	(38)	(56)
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax	(32)	58	82
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	192	33	(39)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	92	147	99
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	100	(114)	(138)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax and reclassification adjustments		5	(39)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax		(1)	42
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax	12	6	(81)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment before reclassification adjustments, Tax		(2)	13
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Tax		0	(20)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	(4)	(2)	33
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period before reclassification adjustments, Net of Tax	8	3	(26)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0	(1)	22
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	8	4	(48)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax [Abstract]
Other Comprehensive Income Unrealized Gain Loss On Net Investment Hedges Arising During the Period, Before Tax	(10)	1	29
Other Comprehensive Income (Loss), Reclassification Adjustment for Net Investment Hedges Included in Net Income, Discontinued Operation, before Tax			(4)
Other Comprehensive Income (Loss), Net Investment Hedges, before Tax			33
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax Effect [Abstract]
Other Comprehensive Income Unrealized Gain Loss On Net Investment Hedges Arising During the Period, Tax	4	0	(11)
Other Comprehensive Income (Loss), Reclassification Adjustment for Net Investment Hedges Included in Net Income, Discontinued Operation, Tax			1
Other Comprehensive Income (Loss), Net Investment Hedges, Tax			(12)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Other Comprehensive Income Unrealized Gain Loss On Net Investment Hedges Arising During the Period Net of Tax	(6)	1	18
Other Comprehensive Income (Loss), Reclassification Adjustment for Net Investment Hedges Included in Net Income, Discontinued Operation, Net of Tax	0	0	(3)
Other Comprehensive Income (Loss), Net Investment Hedges, Net of Tax	(6)	1	21
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During the Period, Before Tax	5		2
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During the Period, Tax	(2)		(1)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	3	0	1
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Tax [Abstract]
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax	1	(5)	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax		(4)	1
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax		(1)	(1)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Tax [Abstract]
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax	0	2	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax		2	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax		0	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	1	(3)	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax	0	(2)	1
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax	1	(1)	(1)
Other Comprehensive Income (Loss), before Tax [Abstract]
Other Comprehensive Income (Loss), before Tax	140	(166)	(267)
Other Comprehensive Income (Loss), Tax [Abstract]
Other Comprehensive Income (Loss), Tax	(34)	56	102
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other Comprehensive Income (Loss), Net of Tax	$ 106	$ (110)	$ (165)