Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Jan. 01, 2019
Increase in the CET1 capital ratio			0.02%
LIBOR loans percent of portfolio	86.00%
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%
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
Accounting Standards Update 2018-15 [Member]
Hosting fees previously including in outside processing fee expense	$ 7
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