Investment Securities (Summary Of Continuous Unrealized Loss Positions Of Available-For-Sale Security) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Document Period End Date	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Member]
Unrealized Loss Position For - Estimated Fair Value - Less than 12 Months	$ 3,582	$ 28,397
Unrealized Loss Position For - Unrealized Loss - Less than 12 Months	(15)	(554)
Unrealized Loss Position For - Estimated Fair Value - 12 Months or More	20,577	1,719
Unrealized Loss Position For - Unrealized Loss - 12 Months or More	(451)	(68)
Unrealized Loss Position For - Estimated Fair Value - Total	24,159	30,116
Unrealized Loss Position For - Unrealized Loss - Total	$ (466)	$ (622)