Investment Securities (Summary Of Amount Of Gross Unrealized Losses For Debt Securities And Estimated Fair Value) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Investment Securities Gross Unrealized Losses Less Than 12 Months	$ 131	$ 47
Investment Securities Estimated Fair Value Less Than 12 Months	7,188	5,642
Investment Securities Gross Unrealized Losses 12 Months or More	222	147
Investment Securities Estimated Fair Value 12 Months or More	6,431	6,714
Investment Securities Gross Unrealized Losses Total	353	194
Investment Securities Estimated Fair Value Total	13,619	12,356
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Held-to-maturity, Less than 12 months - Gross unrealized losses	5	3
Held-to-maturity, Less than 12 months - Estimated fair value	257	263
Held-to-maturity, 12 months or more - Gross unrealized losses	16	10
Held-to-maturity, 12 months or more - Estimated fair value	300	292
Held-to-maturity, Total - Gross unrealized losses	21	13
Held-to-maturity, Total - Estimated fair value	557	555
Available-for-sale, Less than 12 months - Gross unrealized losses	15	6
Available-for-sale, Less than 12 months - Estimated fair value	873	554
Available-for-sale, 12 months or more - Gross unrealized losses	10	5
Available-for-sale, 12 months or more - Estimated fair value	218	230
Available-for-sale, Total - Gross unrealized losses	25	11
Available-for-sale, Total - Estimated fair value	1,091	784
Agency Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	13	6
Available-for-sale, Less than 12 months - Estimated fair value	885	808
Available-for-sale, 12 months or more - Gross unrealized losses	10	7
Available-for-sale, 12 months or more - Estimated fair value	851	808
Available-for-sale, Total - Gross unrealized losses	23	13
Available-for-sale, Total - Estimated fair value	1,736	1,616
Agency Guaranteed Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	93	29
Available-for-sale, Less than 12 months - Estimated fair value	4,523	3,609
Available-for-sale, 12 months or more - Gross unrealized losses	169	112
Available-for-sale, 12 months or more - Estimated fair value	4,418	4,721
Available-for-sale, Total - Gross unrealized losses	262	141
Available-for-sale, Total - Estimated fair value	8,941	8,330
Small Business Administration Loan-Backed Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	5	3
Available-for-sale, Less than 12 months - Estimated fair value	650	408
Available-for-sale, 12 months or more - Gross unrealized losses	16	12
Available-for-sale, 12 months or more - Estimated fair value	630	649
Available-for-sale, Total - Gross unrealized losses	21	15
Available-for-sale, Total - Estimated fair value	1,280	1,057
Available-for-sale, Unrealized losses, Other [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	0	0
Available-for-sale, Less than 12 months - Estimated fair value	0	0
Available-for-sale, 12 months or more - Gross unrealized losses	1	1
Available-for-sale, 12 months or more - Estimated fair value	14	14
Available-for-sale, Total - Gross unrealized losses	1	1
Available-for-sale, Total - Estimated fair value	14	14
Available-for-sale Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	126	44
Available-for-sale, Less than 12 months - Estimated fair value	6,931	5,379
Available-for-sale, 12 months or more - Gross unrealized losses	206	137
Available-for-sale, 12 months or more - Estimated fair value	6,131	6,422
Available-for-sale, Total - Gross unrealized losses	332	181
Available-for-sale, Total - Estimated fair value	$ 13,062	$ 11,801