Investment Securities (Gross Unrealized Loss and Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	$ (126)	$ (110)
AFS unrealized loss position less than 12 months - fair value	13,913	17,837
AFS unrealized loss position 12 months or more - unrealized loss	(709)	(336)
AFS unrealized loss position 12 months or more - fair value	23,902	14,697
Total AFS unrealized loss	(835)	(446)
Total AFS fair Value	37,815	32,534
HTM unrealized loss position less than 12 months - unrealized loss	(62)	(25)
HTM unrealized loss position less than 12 months - fair value	4,506	3,445
HTM unrealized loss position 12 months or more - unrealized loss	(349)	(147)
HTM unrealized loss position 12 months or more - fair value	8,490	6,490
Total HTM unrealized loss	(411)	(172)
Total HTM fair value	12,996	9,935
US Treasury and Government Agencies Securities
Debt Securities, Available-for-sale [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(21)	(42)
AFS unrealized loss position less than 12 months - fair value	4,125	6,099
AFS unrealized loss position 12 months or more - unrealized loss	(116)	(42)
AFS unrealized loss position 12 months or more - fair value	5,423	1,465
Total AFS unrealized loss	(137)	(84)
Total AFS fair Value	9,548	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	(23)	(10)
HTM unrealized loss position 12 months or more - fair value	446	255
Total HTM unrealized loss	(23)	(13)
Total HTM fair value	446	450
Residential mortgage-backed Securities | Mortgage-backed Securities Agency
Debt Securities, Available-for-sale [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(57)	(47)
AFS unrealized loss position less than 12 months - fair value	4,823	8,151
AFS unrealized loss position 12 months or more - unrealized loss	(467)	(202)
AFS unrealized loss position 12 months or more - fair value	13,830	9,954
Total AFS unrealized loss	(524)	(249)
Total AFS fair Value	18,653	18,105
HTM unrealized loss position less than 12 months - unrealized loss	(58)	(10)
HTM unrealized loss position less than 12 months - fair value	4,191	3,167
HTM unrealized loss position 12 months or more - unrealized loss	(300)	(129)
HTM unrealized loss position 12 months or more - fair value	7,921	6,168
Total HTM unrealized loss	(358)	(139)
Total HTM fair value	12,112	9,335
Residential mortgage-backed Securities | Mortgage-backed Securities Non-agency
Debt Securities, Available-for-sale [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(1)
AFS unrealized loss position less than 12 months - fair value	74
AFS unrealized loss position 12 months or more - unrealized loss	(12)	(21)
AFS unrealized loss position 12 months or more - fair value	310	383
Total AFS unrealized loss	(13)	(21)
Total AFS fair Value	384	383
Commercial Mortgage Backed Securities | Mortgage-backed Securities Agency
Debt Securities, Available-for-sale [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(1)	(11)
AFS unrealized loss position less than 12 months - fair value	65	524
AFS unrealized loss position 12 months or more - unrealized loss	(65)	(47)
AFS unrealized loss position 12 months or more - fair value	1,516	1,302
Total AFS unrealized loss	(66)	(58)
Total AFS fair Value	1,581	1,826
HTM unrealized loss position less than 12 months - unrealized loss	(1)
HTM unrealized loss position less than 12 months - fair value	88
Total HTM unrealized loss	(1)
Total HTM fair value	88
Commercial Mortgage Backed Securities | Mortgage-backed Securities Non-agency
Debt Securities, Available-for-sale [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(23)	(3)
AFS unrealized loss position less than 12 months - fair value	1,809	400
AFS unrealized loss position 12 months or more - unrealized loss	(14)	(6)
AFS unrealized loss position 12 months or more - fair value	498	333
Total AFS unrealized loss	(37)	(9)
Total AFS fair Value	2,307	733
HTM unrealized loss position less than 12 months - unrealized loss	(1)
HTM unrealized loss position less than 12 months - fair value	152
Total HTM unrealized loss	(1)
Total HTM fair value	152
Asset backed
Debt Securities, Available-for-sale [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(11)	(4)
AFS unrealized loss position less than 12 months - fair value	2,149	1,697
AFS unrealized loss position 12 months or more - unrealized loss	(9)	(4)
AFS unrealized loss position 12 months or more - fair value	1,032	462
Total AFS unrealized loss	(20)	(8)
Total AFS fair Value	3,181	2,159
Other debt
Debt Securities, Available-for-sale [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(12)	(3)
AFS unrealized loss position less than 12 months - fair value	868	966
AFS unrealized loss position 12 months or more - unrealized loss	(26)	(14)
AFS unrealized loss position 12 months or more - fair value	1,293	798
Total AFS unrealized loss	(38)	(17)
Total AFS fair Value	2,161	1,764
HTM unrealized loss position less than 12 months - unrealized loss	(2)	(12)
HTM unrealized loss position less than 12 months - fair value	75	83
HTM unrealized loss position 12 months or more - unrealized loss	(26)	(8)
HTM unrealized loss position 12 months or more - fair value	123	67
Total HTM unrealized loss	(28)	(20)
Total HTM fair value	$ 198	$ 150