Investment Securities (Gross Unrealized Loss and Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Millions	Sep. 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	$ (19)	$ (126)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	4,506	13,913
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(87)	(709)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	8,596	23,902
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(106)	(835)
Debt securities, available-for-sale, unrealized loss position	13,102	37,815
HTM unrealized loss position less than 12 months - unrealized loss	(1)	(62)
HTM unrealized loss position less than 12 months - fair value	27	4,506
HTM unrealized loss position 12 months or more - unrealized loss	(49)	(349)
HTM unrealized loss position 12 months or more - fair value	3,828	8,490
Total HTM unrealized loss	(50)	(411)
Total HTM fair value	3,855	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	(11)	(21)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	2,300	4,125
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(1)	(116)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	248	5,423
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(12)	(137)
Debt securities, available-for-sale, unrealized loss position	2,548	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	(5)	(57)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	1,329	4,823
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(51)	(467)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	5,471	13,830
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(56)	(524)
Debt securities, available-for-sale, unrealized loss position	6,800	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	(34)	(300)
HTM unrealized loss position 12 months or more - fair value	3,709	7,921
Total HTM unrealized loss	(34)	(358)
Total HTM fair value	3,709	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 - fair value		74
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(3)	(12)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	242	310
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(3)	(13)
Debt securities, available-for-sale, unrealized loss position	242	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 - fair value		65
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(24)	(65)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	1,121	1,516
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(24)	(66)
Debt securities, available-for-sale, unrealized loss position	1,121	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 - fair value	413	1,809
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(3)	(14)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	217	498
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(4)	(37)
Debt securities, available-for-sale, unrealized loss position	630	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	(2)	(11)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	464	2,149
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(4)	(9)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	794	1,032
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(6)	(20)
Debt securities, available-for-sale, unrealized loss position	1,258	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 - fair value		868
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(1)	(26)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	503	1,293
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(1)	(38)
Debt securities, available-for-sale, unrealized loss position	503	2,161
HTM unrealized loss position less than 12 months - unrealized loss	(1)	(2)
HTM unrealized loss position less than 12 months - fair value	27	75
HTM unrealized loss position 12 months or more - unrealized loss	(15)	(26)
HTM unrealized loss position 12 months or more - fair value	119	123
Total HTM unrealized loss	(16)	(28)
Total HTM fair value	$ 146	$ 198