Accumulated Other Comprehensive (Loss) Income (Before and After Tax) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
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	$ 132	$ 185	$ 183	$ 465
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	23	39	50	93
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent	109	146	133	372
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	(37)	(25)	(42)	(129)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(3)	1	(5)	(19)
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax, Portion Attributable to Parent	(34)	(26)	(37)	(110)
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	95	160	141	336
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	20	40	45	74
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent	75	120	96	262
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	4	(1)	6	12
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax		(1)		(1)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent		0		13
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	(1)	0	(2)	(5)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Tax		0		0
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Parent		0		(5)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	3	(1)	4	7
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax		(1)		(1)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent		0		8
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	(4)		(6)	(6)
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During the Period, Before Tax	1		1
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	1		2	3
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During the Period, Tax	0		0
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	(3)		(4)	(3)
Other Comprehensive Income Unrealized Gain Loss On Net Cash Flow Hedges Arising During the Period Net of Tax	1		1
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax, [Abstract]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax			(1)	(1)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax [Abstract]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Tax			0	0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Net of Tax			(1)	(1)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent	110	146	133	378
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent	(34)	(26)	(37)	(112)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	$ 76	$ 120	$ 96	$ 266