Accumulated Other Comprehensive Income (Reclassification Out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax	$ 247	$ 138	$ (543)	$ 907
Other comprehensive income (loss), tax effect	(58)	(29)	128	(215)
Other comprehensive income (loss), net of tax	189	109	(415)	692
Investment securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized gains (losses) arising during the period, before tax	276	175	(460)	877
Net unrealized gains (losses) arising during the period, tax	(65)	(38)	109	(206)
Net unrealized gains (losses) arising during the period, net of tax	211	137	(351)	671
Net realized gains reclassified to income from continuing operations, before tax	6	19	38	124
Net realized gains reclassified to income from continuing operations, tax	(1)	(4)	(8)	(28)
Net realized gains reclassified to income from continuing operations, net of tax	5	15	30	96
Other comprehensive income (loss), before tax	270	156	(498)	753
Other comprehensive income (loss), tax effect	(64)	(34)	117	(178)
Other comprehensive income (loss), net of tax	206	122	(381)	575
Translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax	2	6	5	(7)
Other comprehensive income (loss), tax effect	0	(1)	(1)	2
Other comprehensive income (loss), net of tax	2	5	4	(5)
Net investment hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax	(3)	(5)	(5)	7
Other comprehensive income (loss), tax effect	1	1	2	(2)
Other comprehensive income (loss), net of tax	(2)	(4)	(3)	5
Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized gains (losses) arising during the period, before tax				169
Net unrealized gains (losses) arising during the period, tax				(41)
Net unrealized gains (losses) arising during the period, net of tax				128
Net realized gains reclassified to income from continuing operations, before tax	22	19	43	19
Net realized gains reclassified to income from continuing operations, tax	(5)	(5)	(9)	(5)
Net realized gains reclassified to income from continuing operations, net of tax	$ 17	$ 14	34	14
Other comprehensive income (loss), before tax				150
Other comprehensive income (loss), tax effect				(36)
Other comprehensive income (loss), net of tax				114
Defined benefit pension plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax			(2)	4
Other comprehensive income (loss), tax effect			1	(1)
Other comprehensive income (loss), net of tax			$ (1)	$ 3