Accumulated Other Comprehensive (Loss) Income (Rollforward) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018	Jan. 01, 2017
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax [Abstract]
Accumulated other comprehensive income (loss), investment securities, adjustment, after tax	$ 208	$ (481)	$ (173)	$ (473)	$ (186)	$ (273)
Other comprehensive income (loss), investment securities, net change, after tax	681	(295)	100
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	18	16	18	20	14
Other comprehensive income (loss), foreign currency translation adjustment, net of tax	1	(2)	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	2	19	11	19	11	8
Other comprehensive income (loss), cash flow hedges, net change, after tax	(17)	8	3
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), defined benefit pension plans, after tax	(106)	(95)	(89)	(95)	(95)	(90)
Other comprehensive (income) loss, defined benefit plan, after reclassification adjustment, after tax	(11)	0	1
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Total accumulated other comprehensive loss, net of tax	(123)	539	235	531	250	$ 341
Other comprehensive income (loss), net of tax	$ 654	$ (289)	$ 106
Accounting Standards Update 2016-01
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax [Abstract]
Accumulated other comprehensive income (loss), investment securities, adjustment, after tax					27
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
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
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), defined benefit pension plans, after tax					0
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Total accumulated other comprehensive loss, net of tax					(27)
Accounting Standards Update 2018-02
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax [Abstract]
Accumulated other comprehensive income (loss), investment securities, adjustment, after tax					(40)
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
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
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), defined benefit pension plans, after tax					(6)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Total accumulated other comprehensive loss, net of tax					$ 42
Accounting Standards Update 2017-08
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax [Abstract]
Accumulated other comprehensive income (loss), investment securities, adjustment, after tax				8
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
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
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), defined benefit pension plans, after tax				0
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Total accumulated other comprehensive loss, net of tax				$ (8)