Investment Securities (Gross Unrealized Loss and Fair Value of Securities Available for Sale) (Details) - Debt Securities [Member] - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	$ (509)	$ (110)
AFS unrealized loss position less than 12 months - fair value	27,588	17,837
AFS unrealized loss position 12 months or more - unrealized loss	(562)	(336)
AFS unrealized loss position 12 months or more - fair value	12,432	14,697
Total AFS unrealized loss	(1,071)	(446)
Total AFS fair value	40,020	32,534
HTM unrealized loss position less than 12 months - unrealized loss	(188)	(25)
HTM unrealized loss position less than 12 months - fair value	8,195	3,445
HTM unrealized loss position 12 months or more - unrealized loss	(317)	(147)
HTM unrealized loss position 12 months or more - fair value	5,929	6,490
Total HTM unrealized loss	(505)	(172)
Total HTM fair value	14,124	9,935
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(155)	(42)
AFS unrealized loss position less than 12 months - fair value	8,190	6,099
AFS unrealized loss position 12 months or more - unrealized loss	(69)	(42)
AFS unrealized loss position 12 months or more - fair value	1,286	1,465
Total AFS unrealized loss	(224)	(84)
Total AFS fair value	9,476	7,564
HTM unrealized loss position less than 12 months - unrealized loss	(8)	(3)
HTM unrealized loss position less than 12 months - fair value	190	195
HTM unrealized loss position 12 months or more - unrealized loss	(22)	(10)
HTM unrealized loss position 12 months or more - fair value	246	255
Total HTM unrealized loss	(30)	(13)
Total HTM fair value	436	450
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(279)	(47)
AFS unrealized loss position less than 12 months - fair value	13,151	8,151
AFS unrealized loss position 12 months or more - unrealized loss	(381)	(202)
AFS unrealized loss position 12 months or more - fair value	8,462	9,954
Total AFS unrealized loss	(660)	(249)
Total AFS fair value	21,613	18,105
HTM unrealized loss position less than 12 months - unrealized loss	(171)	(10)
HTM unrealized loss position less than 12 months - fair value	7,605	3,167
HTM unrealized loss position 12 months or more - unrealized loss	(275)	(129)
HTM unrealized loss position 12 months or more - fair value	5,582	6,168
Total HTM unrealized loss	(446)	(139)
Total HTM fair value	13,187	9,335
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(1)
AFS unrealized loss position less than 12 months - fair value	57
AFS unrealized loss position 12 months or more - unrealized loss	(13)	(21)
AFS unrealized loss position 12 months or more - fair value	332	383
Total AFS unrealized loss	(14)	(21)
Total AFS fair value	389	383
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(18)	(11)
AFS unrealized loss position less than 12 months - fair value	533	524
AFS unrealized loss position 12 months or more - unrealized loss	(65)	(47)
AFS unrealized loss position 12 months or more - fair value	1,189	1,302
Total AFS unrealized loss	(83)	(58)
Total AFS fair value	1,722	1,826
HTM unrealized loss position less than 12 months - unrealized loss	(2)
HTM unrealized loss position less than 12 months - fair value	127
Total HTM unrealized loss	(2)
Total HTM fair value	127
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(19)	(3)
AFS unrealized loss position less than 12 months - fair value	1,403	400
AFS unrealized loss position 12 months or more - unrealized loss	(10)	(6)
AFS unrealized loss position 12 months or more - fair value	199	333
Total AFS unrealized loss	(29)	(9)
Total AFS fair value	1,602	733
HTM unrealized loss position less than 12 months - unrealized loss	(1)
HTM unrealized loss position less than 12 months - fair value	176
Total HTM unrealized loss	(1)
Total HTM fair value	176
Asset backed [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(15)	(4)
AFS unrealized loss position less than 12 months - fair value	2,626	1,697
AFS unrealized loss position 12 months or more - unrealized loss	(3)	(4)
AFS unrealized loss position 12 months or more - fair value	301	462
Total AFS unrealized loss	(18)	(8)
Total AFS fair value	2,927	2,159
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(22)	(3)
AFS unrealized loss position less than 12 months - fair value	1,628	966
AFS unrealized loss position 12 months or more - unrealized loss	(21)	(14)
AFS unrealized loss position 12 months or more - fair value	663	798
Total AFS unrealized loss	(43)	(17)
Total AFS fair value	2,291	1,764
HTM unrealized loss position less than 12 months - unrealized loss	(6)	(12)
HTM unrealized loss position less than 12 months - fair value	97	83
HTM unrealized loss position 12 months or more - unrealized loss	(20)	(8)
HTM unrealized loss position 12 months or more - fair value	101	67
Total HTM unrealized loss	(26)	(20)
Total HTM fair value	$ 198	$ 150