Investment Securities (Summary Of Investment Securities In Unrealized Loss Positions) (Details) - USD ($) $ in Millions		Mar. 31, 2020	Dec. 31, 2019
Temporarily Impaired Less than 12 months, Fair Value		$ 110	$ 1,494
Temporarily Impaired Less than 12 Months, Unrealized Losses		0	7
Temporarily Impaired 12 months or more, Fair Value		0	1,906
Temporarily Impaired 12 Months or more, Unrealized Losses		0	21
Temporarily Impaired Total, Fair Value		110	3,400
Temporarily Impaired Total, Unrealized Losses		0	28
Residential mortgage-backed securities
Temporarily Impaired Less than 12 months, Fair Value	[1]	110	1,494
Temporarily Impaired Less than 12 Months, Unrealized Losses	[1]	0	7
Temporarily Impaired 12 months or more, Fair Value	[1]	0	1,906
Temporarily Impaired 12 Months or more, Unrealized Losses	[1]	0	21
Temporarily Impaired Total, Fair Value	[1]	110	3,400
Temporarily Impaired Total, Unrealized Losses	[1]	$ 0	$ 28

[1] Issued and/or guaranteed by U.S. government agencies or U.S. government-sponsored enterprises.