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, 2017	Dec. 31, 2016
Investment [Line Items]
Investment Securities Gross Unrealized Losses Less Than 12 Months	$ 141	$ 157
Investment Securities Estimated Fair Value Less Than 12 Months	10,184	9,585
Investment Securities Gross Unrealized Losses 12 Months or More	35	33
Investment Securities Estimated Fair Value 12 Months or More	1,517	1,378
Investment Securities Gross Unrealized Losses Total	176	190
Investment Securities Estimated Fair Value Total	11,701	10,963
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Held-to-maturity, Less than 12 months - Gross unrealized losses	10	15
Held-to-maturity, Less than 12 months - Estimated fair value	309	467
Held-to-maturity, 12 months or more - Gross unrealized losses	9	8
Held-to-maturity, 12 months or more - Estimated fair value	128	61
Held-to-maturity, Total - Gross unrealized losses	19	23
Held-to-maturity, Total - Estimated fair value	437	528
Available-for-sale, Less than 12 months - Gross unrealized losses	17	28
Available-for-sale, Less than 12 months - Estimated fair value	811	992
Available-for-sale, 12 months or more - Gross unrealized losses	1	0
Available-for-sale, 12 months or more - Estimated fair value	14	9
Available-for-sale, Total - Gross unrealized losses	18	28
Available-for-sale, Total - Estimated fair value	825	1,001
Agency Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	7	9
Available-for-sale, Less than 12 months - Estimated fair value	1,297	950
Available-for-sale, 12 months or more - Gross unrealized losses	1	0
Available-for-sale, 12 months or more - Estimated fair value	124	127
Available-for-sale, Total - Gross unrealized losses	8	9
Available-for-sale, Total - Estimated fair value	1,421	1,077
Agency Guaranteed Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	103	102
Available-for-sale, Less than 12 months - Estimated fair value	7,220	6,649
Available-for-sale, 12 months or more - Gross unrealized losses	8	7
Available-for-sale, 12 months or more - Estimated fair value	440	326
Available-for-sale, Total - Gross unrealized losses	111	109
Available-for-sale, Total - Estimated fair value	7,660	6,975
Small Business Administration Loan-Backed Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	4	3
Available-for-sale, Less than 12 months - Estimated fair value	547	527
Available-for-sale, 12 months or more - Gross unrealized losses	15	16
Available-for-sale, 12 months or more - Estimated fair value	798	841
Available-for-sale, Total - Gross unrealized losses	19	19
Available-for-sale, Total - Estimated fair value	1,345	1,368
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	2
Available-for-sale, 12 months or more - Estimated fair value	13	14
Available-for-sale, Total - Gross unrealized losses	1	2
Available-for-sale, Total - Estimated fair value	13	14
Available-for-sale Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	131	142
Available-for-sale, Less than 12 months - Estimated fair value	9,875	9,118
Available-for-sale, 12 months or more - Gross unrealized losses	26	25
Available-for-sale, 12 months or more - Estimated fair value	1,389	1,317
Available-for-sale, Total - Gross unrealized losses	157	167
Available-for-sale, Total - Estimated fair value	$ 11,264	$ 10,435