Accumulated Other Comprehensive (Loss) Income (Before and After Tax) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Tax	$ (157)	$ 140	$ 750	$ 944
Other comprehensive income (loss), tax effect	37	(34)	(178)	(223)
Other Comprehensive Income (Loss), Net of Tax	(120)	106	572	721
Investment Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(92)	165	785	990
Other Comprehensive Income (Loss) before Reclassifications, Tax	22	(39)	(184)	(233)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(70)	126	601	757
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	43	27	167	60
Reclassification from AOCI, Current Period, Tax	(10)	(6)	(38)	(14)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	33	21	129	46
Other Comprehensive Income (Loss), before Tax	(135)	138	618	930
Other comprehensive income (loss), tax effect	32	(33)	(146)	(219)
Other Comprehensive Income (Loss), Net of Tax	(103)	105	472	711
Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Tax	3	(2)	(4)	4
Other comprehensive income (loss), tax effect	(1)	1	1	(1)
Other Comprehensive Income (Loss), Net of Tax	2	(1)	(3)	3
Net Investment Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Tax	(4)	2	3	(3)
Other comprehensive income (loss), tax effect	1	(1)	(1)	1
Other Comprehensive Income (Loss), Net of Tax	(3)	1	2	(2)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax		5	169	26
Other Comprehensive Income (Loss) before Reclassifications, Tax		(1)	(41)	(6)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		4	128	20
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	21	3	40	12
Reclassification from AOCI, Current Period, Tax	(5)	0	(10)	(2)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 16	3	30	10
Other Comprehensive Income (Loss), before Tax		2	129	14
Other comprehensive income (loss), tax effect		(1)	(31)	(4)
Other Comprehensive Income (Loss), Net of Tax		$ 1	98	10
Defined benefit pension plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Tax			4	(1)
Other comprehensive income (loss), tax effect			(1)	0
Other Comprehensive Income (Loss), Net of Tax			$ 3	$ (1)