Investment Securities (Proceeds and Gross Realized Gains And Losses from Sales of Securities Available for Sale) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Proceeds	[1]	$ 4,801	$ 24,495	$ 115
Gross realized gains		5	16	0
Gross realized losses		$ 1	$ 10	$ 0

[1] Certain prior year amounts have been reclassified to conform to the current year presentation. See Note 1 for additional information.