Investment Securities (Summary Of Agency Securities Estimated Weighted Average Life Classifications) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Agency securities classified as available for sale, Fair value	$ 71,776	$ 100,442
Agency securities classified as available for sale, Amortized cost	$ 69,343	$ 98,670
Weighted Average Coupon	3.84%	3.68%
Weighted Average Yield	2.93%	3.07%
Less Than or Equal to Three Years [Member]
Fair Value	$ 2,790	$ 2,671
Amortized Cost	$ 2,866	$ 2,654
Weighted Average Coupon	3.49%	3.54%
Weighted Average Yield	2.31%	2.61%
Greater Than Three Years and Less Than or Equal to Five Years [Member]
Fair Value	$ 23,997	$ 10,822
Amortized Cost	$ 23,169	$ 10,563
Weighted Average Coupon	4.04%	3.85%
Weighted Average Yield	2.96%	3.20%
Greater Than Five Years [Member]
Fair Value	$ 44,910	$ 86,492
Amortized Cost	$ 43,213	$ 85,002
Weighted Average Coupon	3.75%	3.67%
Weighted Average Yield	2.95%	3.07%
Greater Than Ten Years [Member]
Fair Value	$ 79	$ 457
Amortized Cost	$ 95	$ 451
Weighted Average Coupon	3.50%	3.31%
Weighted Average Yield	3.60%	3.06%