Investment Securities (Gross Unrealized Loss and Fair Value of Securities Available for Sale) (Details) - Debt Securities [Member] - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	$ (574)	$ (110)
AFS unrealized loss position less than 12 months - fair value	30,327	17,837
AFS unrealized loss position 12 months or more - unrealized loss	(753)	(336)
AFS unrealized loss position 12 months or more - fair value	14,849	14,697
Total AFS unrealized loss	(1,327)	(446)
Total AFS fair value	45,176	32,534
HTM unrealized loss position less than 12 months - unrealized loss	(242)	(25)
HTM unrealized loss position less than 12 months - fair value	9,183	3,445
HTM unrealized loss position 12 months or more - unrealized loss	(400)	(147)
HTM unrealized loss position 12 months or more - fair value	6,328	6,490
Total HTM unrealized loss	(642)	(172)
Total HTM fair value	15,511	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	(177)	(42)
AFS unrealized loss position less than 12 months - fair value	8,745	6,099
AFS unrealized loss position 12 months or more - unrealized loss	(117)	(42)
AFS unrealized loss position 12 months or more - fair value	2,253	1,465
Total AFS unrealized loss	(294)	(84)
Total AFS fair value	10,998	7,564
HTM unrealized loss position less than 12 months - unrealized loss		(3)
HTM unrealized loss position less than 12 months - fair value		195
HTM unrealized loss position 12 months or more - unrealized loss	(38)	(10)
HTM unrealized loss position 12 months or more - fair value	429	255
Total HTM unrealized loss	(38)	(13)
Total HTM fair value	429	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	(331)	(47)
AFS unrealized loss position less than 12 months - fair value	15,278	8,151
AFS unrealized loss position 12 months or more - unrealized loss	(507)	(202)
AFS unrealized loss position 12 months or more - fair value	9,409	9,954
Total AFS unrealized loss	(838)	(249)
Total AFS fair value	24,687	18,105
HTM unrealized loss position less than 12 months - unrealized loss	(232)	(10)
HTM unrealized loss position less than 12 months - fair value	8,631	3,167
HTM unrealized loss position 12 months or more - unrealized loss	(341)	(129)
HTM unrealized loss position 12 months or more - fair value	5,797	6,168
Total HTM unrealized loss	(573)	(139)
Total HTM fair value	14,428	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	105
AFS unrealized loss position 12 months or more - unrealized loss	(12)	(21)
AFS unrealized loss position 12 months or more - fair value	308	383
Total AFS unrealized loss	(13)	(21)
Total AFS fair value	413	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	(8)	(11)
AFS unrealized loss position less than 12 months - fair value	412	524
AFS unrealized loss position 12 months or more - unrealized loss	(77)	(47)
AFS unrealized loss position 12 months or more - fair value	1,473	1,302
Total AFS unrealized loss	(85)	(58)
Total AFS fair value	1,885	1,826
HTM unrealized loss position less than 12 months - unrealized loss	(2)
HTM unrealized loss position less than 12 months - fair value	64
Total HTM unrealized loss	(2)
Total HTM fair value	64
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	1,128	400
AFS unrealized loss position 12 months or more - unrealized loss	(10)	(6)
AFS unrealized loss position 12 months or more - fair value	196	333
Total AFS unrealized loss	(29)	(9)
Total AFS fair value	1,324	733
HTM unrealized loss position less than 12 months - unrealized loss	(1)
HTM unrealized loss position less than 12 months - fair value	344
Total HTM unrealized loss	(1)
Total HTM fair value	344
Asset backed [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(14)	(4)
AFS unrealized loss position less than 12 months - fair value	3,095	1,697
AFS unrealized loss position 12 months or more - unrealized loss	(3)	(4)
AFS unrealized loss position 12 months or more - fair value	372	462
Total AFS unrealized loss	(17)	(8)
Total AFS fair value	3,467	2,159
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(24)	(3)
AFS unrealized loss position less than 12 months - fair value	1,564	966
AFS unrealized loss position 12 months or more - unrealized loss	(27)	(14)
AFS unrealized loss position 12 months or more - fair value	838	798
Total AFS unrealized loss	(51)	(17)
Total AFS fair value	2,402	1,764
HTM unrealized loss position less than 12 months - unrealized loss	(7)	(12)
HTM unrealized loss position less than 12 months - fair value	144	83
HTM unrealized loss position 12 months or more - unrealized loss	(21)	(8)
HTM unrealized loss position 12 months or more - fair value	102	67
Total HTM unrealized loss	(28)	(20)
Total HTM fair value	$ 246	$ 150