Investment Securities (Gross Unrealized Loss and Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Millions	Mar. 31, 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	4,838	13,913
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(408)	(709)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	25,072	23,902
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(420)	(835)
Debt securities, available-for-sale, unrealized loss position	29,910	37,815
HTM unrealized loss position less than 12 months - unrealized loss	(1)	(62)
HTM unrealized loss position less than 12 months - fair value	38	4,506
HTM unrealized loss position 12 months or more - unrealized loss	(217)	(349)
HTM unrealized loss position 12 months or more - fair value	10,375	8,490
Total HTM unrealized loss	(218)	(411)
Total HTM fair value	10,413	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	(2)	(21)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	1,699	4,125
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(65)	(116)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	5,908	5,423
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(67)	(137)
Debt securities, available-for-sale, unrealized loss position	7,607	9,548
HTM unrealized loss position 12 months or more - unrealized loss	(11)	(23)
HTM unrealized loss position 12 months or more - fair value	460	446
Total HTM unrealized loss	(11)	(23)
Total HTM fair value	460	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	(2)	(57)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	1,230	4,823
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(248)	(467)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	14,184	13,830
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(250)	(524)
Debt securities, available-for-sale, unrealized loss position	15,414	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	(185)	(300)
HTM unrealized loss position 12 months or more - fair value	9,778	7,921
Total HTM unrealized loss	(185)	(358)
Total HTM fair value	9,778	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	(11)	(12)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	332	310
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(11)	(13)
Debt securities, available-for-sale, unrealized loss position	332	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	(52)	(65)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	1,500	1,516
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(52)	(66)
Debt securities, available-for-sale, unrealized loss position	1,500	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	(3)	(23)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	801	1,809
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(12)	(14)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	646	498
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(15)	(37)
Debt securities, available-for-sale, unrealized loss position	1,447	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	(5)	(11)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	1,108	2,149
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(6)	(9)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	1,178	1,032
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(11)	(20)
Debt securities, available-for-sale, unrealized loss position	2,286	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	(14)	(26)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	1,324	1,293
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(14)	(38)
Debt securities, available-for-sale, unrealized loss position	1,324	2,161
HTM unrealized loss position less than 12 months - unrealized loss	(1)	(2)
HTM unrealized loss position less than 12 months - fair value	38	75
HTM unrealized loss position 12 months or more - unrealized loss	(21)	(26)
HTM unrealized loss position 12 months or more - fair value	137	123
Total HTM unrealized loss	(22)	(28)
Total HTM fair value	$ 175	$ 198