Accumulated Other Comprehensive Income (Loss) (Rollforward) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax [Abstract]
Accumulated other comprehensive income (loss), investment securities, adjustment, after tax	$ 640	$ 208	$ (481)	$ (173)
Other comprehensive income (loss), investment securities, net change, after tax	432	681	(295)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), translation adjustment, net of tax	19	19	18	16
Translation adjustments and net investment hedges, net change	0	1	(2)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract]
Accumulated other comprehensive income (loss), cumulative changes in net gain (loss) from cash flow hedges, net of tax	82	2	19	11
Other comprehensive income (loss), cash flow hedges, net change, after tax	80	(17)	8
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), defined benefit pension plans, after tax	(110)	(106)	(95)	(89)
Other comprehensive (income) loss, defined benefit plan, after reclassification adjustment, after tax	(4)	(11)	0
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Total accumulated other comprehensive loss, net of tax	(631)	(123)	539	235
Other comprehensive income, net of tax	$ 508	$ 654	(289)
Cumulative Effect, Period of Adoption, Adjusted Balance
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax [Abstract]
Accumulated other comprehensive income (loss), investment securities, adjustment, after tax			(473)	(186)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), translation adjustment, net of tax			18	20
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract]
Accumulated other comprehensive income (loss), cumulative changes in net gain (loss) from cash flow hedges, net of tax			19	11
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), defined benefit pension plans, after tax			(95)	(95)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Total accumulated other comprehensive loss, net of tax			531	250
Accounting Standards Update 2016-01 | Revision of Prior Period, Accounting Standards Update, Adjustment | Investment Securities
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax [Abstract]
Accumulated other comprehensive income (loss), investment securities, adjustment, after tax				27
Accounting Standards Update 2016-01 | Revision of Prior Period, Accounting Standards Update, Adjustment | Translation adjustments and net investment hedges
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), translation adjustment, net of tax				0
Accounting Standards Update 2016-01 | Revision of Prior Period, Accounting Standards Update, Adjustment | Cash Flow Hedges
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract]
Accumulated other comprehensive income (loss), cumulative changes in net gain (loss) from cash flow hedges, net of tax				0
Accounting Standards Update 2016-01 | Revision of Prior Period, Accounting Standards Update, Adjustment | Defined benefit pension plans
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), defined benefit pension plans, after tax				0
Accounting Standards Update 2016-01 | Revision of Prior Period, Accounting Standards Update, Adjustment | Accumulated other comprehensive (loss) income
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Total accumulated other comprehensive loss, net of tax				(27)
Accounting Standards Update 2018-02 | Revision of Prior Period, Accounting Standards Update, Adjustment | Investment Securities
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax [Abstract]
Accumulated other comprehensive income (loss), investment securities, adjustment, after tax				(40)
Accounting Standards Update 2018-02 | Revision of Prior Period, Accounting Standards Update, Adjustment | Translation adjustments and net investment hedges
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), translation adjustment, net of tax				4
Accounting Standards Update 2018-02 | Revision of Prior Period, Accounting Standards Update, Adjustment | Cash Flow Hedges
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract]
Accumulated other comprehensive income (loss), cumulative changes in net gain (loss) from cash flow hedges, net of tax				0
Accounting Standards Update 2018-02 | Revision of Prior Period, Accounting Standards Update, Adjustment | Defined benefit pension plans
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), defined benefit pension plans, after tax				(6)
Accounting Standards Update 2018-02 | Revision of Prior Period, Accounting Standards Update, Adjustment | Accumulated other comprehensive (loss) income
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Total accumulated other comprehensive loss, net of tax				$ 42
Accounting Standards Update 2017-08 | Revision of Prior Period, Accounting Standards Update, Adjustment | Investment Securities
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax [Abstract]
Accumulated other comprehensive income (loss), investment securities, adjustment, after tax			8
Accounting Standards Update 2017-08 | Revision of Prior Period, Accounting Standards Update, Adjustment | Translation adjustments and net investment hedges
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), translation adjustment, net of tax			0
Accounting Standards Update 2017-08 | Revision of Prior Period, Accounting Standards Update, Adjustment | Cash Flow Hedges
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract]
Accumulated other comprehensive income (loss), cumulative changes in net gain (loss) from cash flow hedges, net of tax			0
Accounting Standards Update 2017-08 | Revision of Prior Period, Accounting Standards Update, Adjustment | Defined benefit pension plans
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), defined benefit pension plans, after tax			0
Accounting Standards Update 2017-08 | Revision of Prior Period, Accounting Standards Update, Adjustment | Accumulated other comprehensive (loss) income
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Total accumulated other comprehensive loss, net of tax			$ (8)