Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Narrative) (Details) - USD ($) $ in Millions			3 Months Ended	9 Months Ended
	Jan. 01, 2020	Jan. 01, 2019	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Increase in the CET1 capital ratio					0.02%
Increase in retail loans allowance for credit losses	$ 25
LIBOR loans percent of portfolio			72.00%	72.00%
Overall allowance for credit losses					$ 668
Cumulative effect of change in accounting principle	13	$ (14)
Business loans percent of portfolio					91.00%
Percent of loan portfolio with interest rate swaps to convert variable-LBIOR to fixed rates			10.00%	10.00%
Accounting Standards Update 2018-15 [Member]
Hosting fees previously including in outside processing fee expense			$ 9	$ 24
Accounting Standards Update 2016-13 [Member]
Day-one decrease in the overall allowance for credit losses	(17)	0
Reduction in business loans allowance for credit losses	(42)	0
Increase in retail loans allowance for credit losses	25	0
Reduction to deferred tax asset	4
Retained Earnings
Cumulative effect of change in accounting principle	13	$ (14)
Retained Earnings | Accounting Standards Update 2016-13 [Member]
Cumulative effect of change in accounting principle	$ 13