Investment Securities (Gains And Losses On Securities) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Securities gains									$ 1	$ 2
Securities losses									(8)	(21)
Net securities losses	$ 1	$ 0	$ 0	$ (8)	$ 0	$ (20)	$ 1	$ 0	$ (7)	$ (19)	$ 0