Investment Securities (Summary Of Amount Of Gross Unrealized Losses For Debt Securities And Estimated Fair Value) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	$ 44	$ 142
Available-for-sale, Less than 12 months - Estimated fair value	5,379	9,118
Available-for-sale, 12 months or more - Gross unrealized losses	137	25
Available-for-sale, 12 months or more - Estimated fair value	6,422	1,317
Available-for-sale, Total - Gross unrealized losses	181	167
Available-for-sale, Total - Estimated fair value	11,801	10,435
Investment Securities Gross Unrealized Losses Less Than 12 Months	47	157
Investment Securities Estimated Fair Value Less Than 12 Months	5,642	9,585
Investment Securities Gross Unrealized Losses 12 Months or More	147	33
Investment Securities Estimated Fair Value 12 Months or More	6,714	1,378
Investment Securities Gross Unrealized Losses Total	194	190
Investment Securities Estimated Fair Value Total	12,356	10,963
Municipal Securities [Member]
Investment [Line Items]
Held-to-maturity, Less than 12 months - Gross unrealized losses	3	15
Held-to-maturity, Less than 12 months - Estimated fair value	263	467
Held-to-maturity, 12 months or more - Gross unrealized losses	10	8
Held-to-maturity, 12 months or more - Estimated fair value	292	61
Held-to-maturity, Total - Gross unrealized losses	13	23
Held-to-maturity, Total - Estimated fair value	555	528
Available-for-sale, Less than 12 months - Gross unrealized losses	6	28
Available-for-sale, Less than 12 months - Estimated fair value	554	992
Available-for-sale, 12 months or more - Gross unrealized losses	5	0
Available-for-sale, 12 months or more - Estimated fair value	230	9
Available-for-sale, Total - Gross unrealized losses	11	28
Available-for-sale, Total - Estimated fair value	784	1,001
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	14	14
Available-for-sale, Total - Gross unrealized losses	1	2
Available-for-sale, Total - Estimated fair value	14	14
Agency Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	6	9
Available-for-sale, Less than 12 months - Estimated fair value	808	950
Available-for-sale, 12 months or more - Gross unrealized losses	7	0
Available-for-sale, 12 months or more - Estimated fair value	808	127
Available-for-sale, Total - Gross unrealized losses	13	9
Available-for-sale, Total - Estimated fair value	1,616	1,077
Agency Guaranteed Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	29	102
Available-for-sale, Less than 12 months - Estimated fair value	3,609	6,649
Available-for-sale, 12 months or more - Gross unrealized losses	112	7
Available-for-sale, 12 months or more - Estimated fair value	4,721	326
Available-for-sale, Total - Gross unrealized losses	141	109
Available-for-sale, Total - Estimated fair value	8,330	6,975
Small Business Administration Loan-Backed Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	3	3
Available-for-sale, Less than 12 months - Estimated fair value	408	527
Available-for-sale, 12 months or more - Gross unrealized losses	12	16
Available-for-sale, 12 months or more - Estimated fair value	649	841
Available-for-sale, Total - Gross unrealized losses	15	19
Available-for-sale, Total - Estimated fair value	$ 1,057	$ 1,368