Investment Securities (Summary Of Amount Of Gross Unrealized Losses For Debt Securities And Estimated Fair Value) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Investment [Line Items]
Investment Securities Gross Unrealized Losses Less Than 12 Months	$ 84	$ 157
Investment Securities Estimated Fair Value Less Than 12 Months	7,460	9,585
Investment Securities Gross Unrealized Losses 12 Months or More	23	33
Investment Securities Estimated Fair Value 12 Months or More	1,460	1,378
Investment Securities Gross Unrealized Losses Total	107	190
Investment Securities Estimated Fair Value Total	8,920	10,963
US States and Political Subdivisions Debt 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	241	467
Held-to-maturity, 12 months or more - Gross unrealized losses	6	8
Held-to-maturity, 12 months or more - Estimated fair value	132	61
Held-to-maturity, Total - Gross unrealized losses	9	23
Held-to-maturity, Total - Estimated fair value	373	528
Available-for-sale, Less than 12 months - Gross unrealized losses	4	28
Available-for-sale, Less than 12 months - Estimated fair value	466	992
Available-for-sale, 12 months or more - Gross unrealized losses	0	0
Available-for-sale, 12 months or more - Estimated fair value	15	9
Available-for-sale, Total - Gross unrealized losses	4	28
Available-for-sale, Total - Estimated fair value	481	1,001
Agency Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	5	9
Available-for-sale, Less than 12 months - Estimated fair value	928	950
Available-for-sale, 12 months or more - Gross unrealized losses	1	0
Available-for-sale, 12 months or more - Estimated fair value	122	127
Available-for-sale, Total - Gross unrealized losses	6	9
Available-for-sale, Total - Estimated fair value	1,050	1,077
Agency Guaranteed Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	71	102
Available-for-sale, Less than 12 months - Estimated fair value	5,693	6,649
Available-for-sale, 12 months or more - Gross unrealized losses	7	7
Available-for-sale, 12 months or more - Estimated fair value	391	326
Available-for-sale, Total - Gross unrealized losses	78	109
Available-for-sale, Total - Estimated fair value	6,084	6,975
Small Business Administration Loan-Backed Securities [Member]
Investment [Line Items]
Available-for-sale, Less than 12 months - Gross unrealized losses	1	3
Available-for-sale, Less than 12 months - Estimated fair value	132	527
Available-for-sale, 12 months or more - Gross unrealized losses	9	16
Available-for-sale, 12 months or more - Estimated fair value	786	841
Available-for-sale, Total - Gross unrealized losses	10	19
Available-for-sale, Total - Estimated fair value	918	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	0	2
Available-for-sale, 12 months or more - Estimated fair value	14	14
Available-for-sale, Total - Gross unrealized losses	0	2
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	81	142
Available-for-sale, Less than 12 months - Estimated fair value	7,219	9,118
Available-for-sale, 12 months or more - Gross unrealized losses	17	25
Available-for-sale, 12 months or more - Estimated fair value	1,328	1,317
Available-for-sale, Total - Gross unrealized losses	98	167
Available-for-sale, Total - Estimated fair value	$ 8,547	$ 10,435