Accumulated Other Comprehensive (Loss) Income (Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax [Abstract]
Accumulated other comprehensive income (loss), investment securities, adjustment, after tax	$ 680	$ 238	$ 680	$ 238	$ 783	$ 208	$ 133	$ (473)	$ (481)
Other comprehensive income (loss), investment securities, net change, after tax	(103)	105	472	711
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	19	18	19	19	19	19	18	18
Other comprehensive income (loss), foreign currency translation adjustment, net of tax	(1)	0	(1)	1
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	100	29	100	29	116	2	28	19	19
Other comprehensive income (loss), cash flow hedges, net change, after tax	(16)	1	98	10
Other Comprehensive Income (Loss), Defined Benefit Plan, Net of Tax [Abstract]
Accumulated other comprehensive income (loss), defined benefit pension plans, after tax	(103)	(96)	(103)	(96)	(103)	(106)	(96)	(95)	(95)
Other comprehensive (income) loss, defined benefit plan, after reclassification adjustment, after tax	0	0	3	(1)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Total accumulated other comprehensive loss, net of tax	(695)	(190)	(695)	(190)	$ (815)	$ (123)	$ (84)	531	$ 539
Other comprehensive income, net of tax	$ (120)	$ 106	$ 572	$ 721
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)