Investment Securities (Gross Unrealized Loss and Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	$ (12)	$ (126)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	4,305	13,913
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(146)	(709)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	13,217	23,902
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(158)	(835)
Debt securities, available-for-sale, unrealized loss position	17,522	37,815
HTM unrealized loss position less than 12 months - unrealized loss	(1)	(62)
HTM unrealized loss position less than 12 months - fair value	31	4,506
HTM unrealized loss position 12 months or more - unrealized loss	(85)	(349)
HTM unrealized loss position 12 months or more - fair value	5,749	8,490
Total HTM unrealized loss	(86)	(411)
Total HTM fair value	5,780	12,996
US Treasury and Government [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(6)	(21)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	2,151	4,125
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(11)	(116)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	2,260	5,423
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(17)	(137)
Debt securities, available-for-sale, unrealized loss position	4,411	9,548
HTM unrealized loss position 12 months or more - unrealized loss		(23)
HTM unrealized loss position 12 months or more - fair value		446
Total HTM unrealized loss		(23)
Total HTM fair value		446
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(1)	(57)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	1,173	4,823
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(89)	(467)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	7,578	13,830
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(90)	(524)
Debt securities, available-for-sale, unrealized loss position	8,751	18,653
HTM unrealized loss position less than 12 months - unrealized loss		(58)
HTM unrealized loss position less than 12 months - fair value		4,191
HTM unrealized loss position 12 months or more - unrealized loss	(68)	(300)
HTM unrealized loss position 12 months or more - fair value	5,619	7,921
Total HTM unrealized loss	(68)	(358)
Total HTM fair value	5,619	12,112
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss		(1)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months		74
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(4)	(12)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	253	310
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(4)	(13)
Debt securities, available-for-sale, unrealized loss position	253	384
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss		(1)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months		65
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(30)	(65)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	1,192	1,516
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(30)	(66)
Debt securities, available-for-sale, unrealized loss position	1,192	1,581
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 [Member] | Mortgage-backed Securities Non-agency [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(1)	(23)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	313	1,809
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(6)	(14)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	224	498
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(7)	(37)
Debt securities, available-for-sale, unrealized loss position	537	2,307
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 [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(4)	(11)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	668	2,149
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(3)	(9)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	942	1,032
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(7)	(20)
Debt securities, available-for-sale, unrealized loss position	1,610	3,181
Other [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss		(12)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months		868
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(3)	(26)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	768	1,293
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(3)	(38)
Debt securities, available-for-sale, unrealized loss position	768	2,161
HTM unrealized loss position less than 12 months - unrealized loss	(1)	(2)
HTM unrealized loss position less than 12 months - fair value	31	75
HTM unrealized loss position 12 months or more - unrealized loss	(17)	(26)
HTM unrealized loss position 12 months or more - fair value	130	123
Total HTM unrealized loss	(18)	(28)
Total HTM fair value	$ 161	$ 198