Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 10,119	$ 17,740
Available for sale, gross unrealized losses less than 12 months	17	110
Available for sale, fair value 12 months or longer	3,853	6,886
Available for sale, gross unrealized losses 12 months or longer	56	208
Available for sale, fair value total	13,972	24,626
Available for sale, gross unrealized losses total	73	318
Held to maturity, fair value less than 12 months	3,828	9,461
Held-to-maturity, gross unrealized losses, less than 12 months	22	155
Held to maturity, fair value 12 months or longer	13,346	23,757
Held to maturity, gross unrealized losses 12 months or longer	86	583
Held to maturity, fair value total	17,174	33,218
Held to maturity, gross unrealized losses total	108	738
US Treasury and federal agencies, mortgage-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,428	5,058
Available for sale, gross unrealized losses less than 12 months	4	21
Available for sale, fair value 12 months or longer	2,618	5,089
Available for sale, gross unrealized losses 12 months or longer	39	160
Available for sale, fair value total	5,046	10,147
Available for sale, gross unrealized losses total	43	181
Held to maturity, fair value less than 12 months	1,166	6,502
Held-to-maturity, gross unrealized losses, less than 12 months	6	103
Held to maturity, fair value 12 months or longer	5,570	10,648
Held to maturity, gross unrealized losses 12 months or longer	46	415
Held to maturity, fair value total	6,736	17,150
Held to maturity, gross unrealized losses total	52	518
Total U.S. Treasury and federal agencies
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,428	5,058
Available for sale, gross unrealized losses less than 12 months	4	21
Available for sale, fair value 12 months or longer	2,618	5,089
Available for sale, gross unrealized losses 12 months or longer	39	160
Available for sale, fair value total	5,046	10,147
Available for sale, gross unrealized losses total	43	181
Held to maturity, fair value less than 12 months	1,942	8,694
Held-to-maturity, gross unrealized losses, less than 12 months	7	148
Held to maturity, fair value 12 months or longer	12,701	23,051
Held to maturity, gross unrealized losses 12 months or longer	69	569
Held to maturity, fair value total	14,643	31,745
Held to maturity, gross unrealized losses total	76	717
Asset-backed securities, student loans
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	10	106
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	183	218
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	193	324
Available for sale, gross unrealized losses total	1	1
Held to maturity, fair value less than 12 months	1,700	481
Held-to-maturity, gross unrealized losses, less than 12 months	13	4
Held to maturity, fair value 12 months or longer	494	536
Held to maturity, gross unrealized losses 12 months or longer	10	6
Held to maturity, fair value total	2,194	1,017
Held to maturity, gross unrealized losses total	23	10
Asset-backed securities, credit cards
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	90	90
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	151	493
Available for sale, gross unrealized losses 12 months or longer	11	26
Available for sale, fair value total	241	583
Available for sale, gross unrealized losses total	11	26
Asset-backed securities, collateralized loan obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	305	548
Available for sale, gross unrealized losses less than 12 months	1	2
Available for sale, fair value 12 months or longer	189	0
Available for sale, gross unrealized losses 12 months or longer	1	0
Available for sale, fair value total	494	548
Available for sale, gross unrealized losses total	2	2
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	405	744
Available for sale, gross unrealized losses less than 12 months	1	2
Available for sale, fair value 12 months or longer	523	711
Available for sale, gross unrealized losses 12 months or longer	13	27
Available for sale, fair value total	928	1,455
Available for sale, gross unrealized losses total	14	29
Held to maturity, fair value less than 12 months	1,700	481
Held-to-maturity, gross unrealized losses, less than 12 months	13	4
Held to maturity, fair value 12 months or longer	494	536
Held to maturity, gross unrealized losses 12 months or longer	10	6
Held to maturity, fair value total	2,194	1,017
Held to maturity, gross unrealized losses total	23	10
Non-U.S. debt securities, mortgage-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	708	1,407
Available for sale, gross unrealized losses less than 12 months	2	4
Available for sale, fair value 12 months or longer	155	118
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	863	1,525
Available for sale, gross unrealized losses total	3	5
Held to maturity, fair value less than 12 months	86	184
Held-to-maturity, gross unrealized losses, less than 12 months	2	2
Held to maturity, fair value 12 months or longer	114	119
Held to maturity, gross unrealized losses 12 months or longer	6	7
Held to maturity, fair value total	200	303
Held to maturity, gross unrealized losses total	8	9
Non-U.S. debt securities, asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	679	1,479
Available for sale, gross unrealized losses less than 12 months	2	6
Available for sale, fair value 12 months or longer	0	0
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	679	1,479
Available for sale, gross unrealized losses total	2	6
Non-U.S. debt securities, government securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	4,635	5,478
Available for sale, gross unrealized losses less than 12 months	6	45
Available for sale, fair value 12 months or longer	0	0
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	4,635	5,478
Available for sale, gross unrealized losses total	6	45
Non-U.S. debt securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,159	2,167
Available for sale, gross unrealized losses less than 12 months	2	12
Available for sale, fair value 12 months or longer	122	226
Available for sale, gross unrealized losses 12 months or longer	0	4
Available for sale, fair value total	1,281	2,393
Available for sale, gross unrealized losses total	2	16
Total non-U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	7,181	10,531
Available for sale, gross unrealized losses less than 12 months	12	67
Available for sale, fair value 12 months or longer	277	344
Available for sale, gross unrealized losses 12 months or longer	1	5
Available for sale, fair value total	7,458	10,875
Available for sale, gross unrealized losses total	13	72
Held to maturity, fair value less than 12 months	86	184
Held-to-maturity, gross unrealized losses, less than 12 months	2	2
Held to maturity, fair value 12 months or longer	114	119
Held to maturity, gross unrealized losses 12 months or longer	6	7
Held to maturity, fair value total	200	303
Held to maturity, gross unrealized losses total	8	9
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	59	365
Available for sale, gross unrealized losses less than 12 months	0	3
Available for sale, fair value 12 months or longer	182	244
Available for sale, gross unrealized losses 12 months or longer	2	4
Available for sale, fair value total	241	609
Available for sale, gross unrealized losses total	2	7
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	0	181
Available for sale, gross unrealized losses less than 12 months	0	3
Available for sale, fair value 12 months or longer	11	14
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	11	195
Available for sale, gross unrealized losses total	0	3
Held to maturity, fair value less than 12 months	100	102
Held-to-maturity, gross unrealized losses, less than 12 months	0	1
Held to maturity, fair value 12 months or longer	37	51
Held to maturity, gross unrealized losses 12 months or longer	1	1
Held to maturity, fair value total	137	153
Held to maturity, gross unrealized losses total	1	2
Other U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	46	861
Available for sale, gross unrealized losses less than 12 months	0	14
Available for sale, fair value 12 months or longer	242	484
Available for sale, gross unrealized losses 12 months or longer	1	12
Available for sale, fair value total	288	1,345
Available for sale, gross unrealized losses total	1	26
US Treasury and federal agencies, direct obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Held to maturity, fair value less than 12 months	776	2,192
Held-to-maturity, gross unrealized losses, less than 12 months	1	45
Held to maturity, fair value 12 months or longer	7,131	12,403
Held to maturity, gross unrealized losses 12 months or longer	23	154
Held to maturity, fair value total	7,907	14,595
Held to maturity, gross unrealized losses total	$ 24	$ 199