Investment Securities (Gross Unrealized Loss and Fair Value of Securities Available for Sale) (Details) - Debt Securities [Member] - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	$ (411)	$ (110)
AFS unrealized loss position less than 12 months - fair value	24,539	17,837
AFS unrealized loss position 12 months or more - unrealized loss	(526)	(336)
AFS unrealized loss position 12 months or more - fair value	13,197	14,697
Total AFS unrealized loss	(937)	(446)
Total AFS fair value	37,736	32,534
HTM unrealized loss position less than 12 months - unrealized loss	(148)	(25)
HTM unrealized loss position less than 12 months - fair value	7,546	3,445
HTM unrealized loss position 12 months or more - unrealized loss	(288)	(147)
HTM unrealized loss position 12 months or more - fair value	6,161	6,490
Total HTM unrealized loss	(436)	(172)
Total HTM fair value	13,707	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	(120)	(42)
AFS unrealized loss position less than 12 months - fair value	6,937	6,099
AFS unrealized loss position 12 months or more - unrealized loss	(59)	(42)
AFS unrealized loss position 12 months or more - fair value	1,142	1,465
Total AFS unrealized loss	(179)	(84)
Total AFS fair value	8,079	7,564
HTM unrealized loss position less than 12 months - unrealized loss	(7)	(3)
HTM unrealized loss position less than 12 months - fair value	191	195
HTM unrealized loss position 12 months or more - unrealized loss	(20)	(10)
HTM unrealized loss position 12 months or more - fair value	246	255
Total HTM unrealized loss	(27)	(13)
Total HTM fair value	437	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	(229)	(47)
AFS unrealized loss position less than 12 months - fair value	11,684	8,151
AFS unrealized loss position 12 months or more - unrealized loss	(355)	(202)
AFS unrealized loss position 12 months or more - fair value	8,965	9,954
Total AFS unrealized loss	(584)	(249)
Total AFS fair value	20,649	18,105
HTM unrealized loss position less than 12 months - unrealized loss	(133)	(10)
HTM unrealized loss position less than 12 months - fair value	7,080	3,167
HTM unrealized loss position 12 months or more - unrealized loss	(249)	(129)
HTM unrealized loss position 12 months or more - fair value	5,830	6,168
Total HTM unrealized loss	(382)	(139)
Total HTM fair value	12,910	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	94
AFS unrealized loss position 12 months or more - unrealized loss	(16)	(21)
AFS unrealized loss position 12 months or more - fair value	352	383
Total AFS unrealized loss	(17)	(21)
Total AFS fair value	446	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	(16)	(11)
AFS unrealized loss position less than 12 months - fair value	499	524
AFS unrealized loss position 12 months or more - unrealized loss	(62)	(47)
AFS unrealized loss position 12 months or more - fair value	1,243	1,302
Total AFS unrealized loss	(78)	(58)
Total AFS fair value	1,742	1,826
HTM unrealized loss position less than 12 months - unrealized loss	(1)
HTM unrealized loss position less than 12 months - fair value	170
Total HTM unrealized loss	(1)
Total HTM fair value	170
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	(15)	(3)
AFS unrealized loss position less than 12 months - fair value	1,284	400
AFS unrealized loss position 12 months or more - unrealized loss	(9)	(6)
AFS unrealized loss position 12 months or more - fair value	325	333
Total AFS unrealized loss	(24)	(9)
Total AFS fair value	1,609	733
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	2,366	1,697
AFS unrealized loss position 12 months or more - unrealized loss	(3)	(4)
AFS unrealized loss position 12 months or more - fair value	383	462
Total AFS unrealized loss	(17)	(8)
Total AFS fair value	2,749	2,159
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(16)	(3)
AFS unrealized loss position less than 12 months - fair value	1,675	966
AFS unrealized loss position 12 months or more - unrealized loss	(22)	(14)
AFS unrealized loss position 12 months or more - fair value	787	798
Total AFS unrealized loss	(38)	(17)
Total AFS fair value	2,462	1,764
HTM unrealized loss position less than 12 months - unrealized loss	(7)	(12)
HTM unrealized loss position less than 12 months - fair value	105	83
HTM unrealized loss position 12 months or more - unrealized loss	(19)	(8)
HTM unrealized loss position 12 months or more - fair value	85	67
Total HTM unrealized loss	(26)	(20)
Total HTM fair value	$ 190	$ 150