Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 14,204	$ 12,428
Available for sale, gross unrealized losses less than 12 months	279	50
Available for sale, fair value 12 months or longer	1,209	2,626
Available for sale, gross unrealized losses 12 months or longer	28	24
Available for sale, fair value total	15,413	15,054
Available for sale, gross unrealized losses total	307	74
Held to maturity, fair value less than 12 months		8,676
Held-to-maturity, gross unrealized losses, less than 12 months		53
Held to maturity, fair value 12 months or longer		4,894
Held to maturity, gross unrealized losses 12 months or longer		42
Held to maturity, fair value total		13,570
Held to maturity, gross unrealized losses total		95
US Treasury and federal agencies, direct obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months		1,430
Available for sale, gross unrealized losses less than 12 months		28
Available for sale, fair value 12 months or longer		0
Available for sale, gross unrealized losses 12 months or longer		0
Available for sale, fair value total		1,430
Available for sale, gross unrealized losses total		28
Held to maturity, fair value less than 12 months	0	604
Held-to-maturity, gross unrealized losses, less than 12 months	0	0
Held to maturity, fair value 12 months or longer	31	2,262
Held to maturity, gross unrealized losses 12 months or longer	0	3
Held to maturity, fair value total	31	2,866
Held to maturity, gross unrealized losses total	0	3
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	2,135	2,499
Available for sale, gross unrealized losses less than 12 months	23	7
Available for sale, fair value 12 months or longer	200	1,665
Available for sale, gross unrealized losses 12 months or longer	2	18
Available for sale, fair value total	2,335	4,164
Available for sale, gross unrealized losses total	25	25
Held to maturity, fair value less than 12 months	955	6,056
Held-to-maturity, gross unrealized losses, less than 12 months	6	31
Held to maturity, fair value 12 months or longer	25	1,606
Held to maturity, gross unrealized losses 12 months or longer	1	13
Held to maturity, fair value total	980	7,662
Held to maturity, gross unrealized losses total	7	44
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	2,135	3,929
Available for sale, gross unrealized losses less than 12 months	23	35
Available for sale, fair value 12 months or longer	200	1,665
Available for sale, gross unrealized losses 12 months or longer	2	18
Available for sale, fair value total	2,335	5,594
Available for sale, gross unrealized losses total	25	53
Held to maturity, fair value less than 12 months	955	6,660
Held-to-maturity, gross unrealized losses, less than 12 months	6	31
Held to maturity, fair value 12 months or longer	56	3,868
Held to maturity, gross unrealized losses 12 months or longer	1	16
Held to maturity, fair value total	1,011	10,528
Held to maturity, gross unrealized losses total	7	47
Asset-backed securities, student loans
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	344	271
Available for sale, gross unrealized losses less than 12 months	11	1
Available for sale, fair value 12 months or longer	99	127
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	443	398
Available for sale, gross unrealized losses total	12	2
Held to maturity, fair value less than 12 months	2,739	2,003
Held-to-maturity, gross unrealized losses, less than 12 months	96	22
Held to maturity, fair value 12 months or longer	1,043	778
Held to maturity, gross unrealized losses 12 months or longer	52	19
Held to maturity, fair value total	3,782	2,781
Held to maturity, gross unrealized losses total	148	41
Asset-backed securities, credit cards
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	85	89
Available for sale, gross unrealized losses less than 12 months	5	1
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	85	89
Available for sale, gross unrealized losses total	5	1
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	1,466	862
Available for sale, gross unrealized losses less than 12 months	76	2
Available for sale, fair value 12 months or longer	292	278
Available for sale, gross unrealized losses 12 months or longer	14	1
Available for sale, fair value total	1,758	1,140
Available for sale, gross unrealized losses total	90	3
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,895	1,222
Available for sale, gross unrealized losses less than 12 months	92	4
Available for sale, fair value 12 months or longer	391	405
Available for sale, gross unrealized losses 12 months or longer	15	2
Available for sale, fair value total	2,286	1,627
Available for sale, gross unrealized losses total	107	6
Held to maturity, fair value less than 12 months	2,739	2,003
Held-to-maturity, gross unrealized losses, less than 12 months	96	22
Held to maturity, fair value 12 months or longer	1,043	778
Held to maturity, gross unrealized losses 12 months or longer	52	19
Held to maturity, fair value total	3,782	2,781
Held to maturity, gross unrealized losses total	148	41
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	1,431	228
Available for sale, gross unrealized losses less than 12 months	15	0
Available for sale, fair value 12 months or longer	203	220
Available for sale, gross unrealized losses 12 months or longer	3	1
Available for sale, fair value total	1,634	448
Available for sale, gross unrealized losses total	18	1
Held to maturity, fair value less than 12 months	35	0
Held-to-maturity, gross unrealized losses, less than 12 months	0	0
Held to maturity, fair value 12 months or longer	122	138
Held to maturity, gross unrealized losses 12 months or longer	14	6
Held to maturity, fair value total	157	138
Held to maturity, gross unrealized losses total	14	6
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	1,741	672
Available for sale, gross unrealized losses less than 12 months	46	1
Available for sale, fair value 12 months or longer	98	109
Available for sale, gross unrealized losses 12 months or longer	6	1
Available for sale, fair value total	1,839	781
Available for sale, gross unrealized losses total	52	2
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	1,044	3,246
Available for sale, gross unrealized losses less than 12 months	18	1
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	1,044	3,246
Available for sale, gross unrealized losses total	18	1
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	3,367	2,736
Available for sale, gross unrealized losses less than 12 months	45	9
Available for sale, fair value 12 months or longer	293	187
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	3,660	2,923
Available for sale, gross unrealized losses total	46	10
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	7,583	6,882
Available for sale, gross unrealized losses less than 12 months	124	11
Available for sale, fair value 12 months or longer	594	516
Available for sale, gross unrealized losses 12 months or longer	10	3
Available for sale, fair value total	8,177	7,398
Available for sale, gross unrealized losses total	134	14
Held to maturity, fair value less than 12 months	35	0
Held-to-maturity, gross unrealized losses, less than 12 months	0	0
Held to maturity, fair value 12 months or longer	122	138
Held to maturity, gross unrealized losses 12 months or longer	14	6
Held to maturity, fair value total	157	138
Held to maturity, gross unrealized losses total	14	6
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	579	163
Available for sale, gross unrealized losses less than 12 months	6	0
Available for sale, fair value 12 months or longer	22	22
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	601	185
Available for sale, gross unrealized losses total	7	1
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	0	13
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	2	4
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	2	17
Available for sale, gross unrealized losses total	0	0
Held to maturity, fair value less than 12 months	39	13
Held-to-maturity, gross unrealized losses, less than 12 months	4	0
Held to maturity, fair value 12 months or longer	20	110
Held to maturity, gross unrealized losses 12 months or longer	3	1
Held to maturity, fair value total	59	123
Held to maturity, gross unrealized losses total	7	1
Total Before MMLF
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Held to maturity, fair value less than 12 months	3,768
Held-to-maturity, gross unrealized losses, less than 12 months	106
Held to maturity, fair value 12 months or longer	1,241
Held to maturity, gross unrealized losses 12 months or longer	70
Held to maturity, fair value total	5,009
Held to maturity, gross unrealized losses total	176
Other U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,012	219
Available for sale, gross unrealized losses less than 12 months	34	0
Available for sale, fair value 12 months or longer	0	14
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	2,012	233
Available for sale, gross unrealized losses total	34	$ 0
Money Market Liquidity Facility
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Held to maturity, fair value less than 12 months	11,080
Held-to-maturity, gross unrealized losses, less than 12 months	13
Held to maturity, fair value 12 months or longer	0
Held to maturity, gross unrealized losses 12 months or longer	0
Held to maturity, fair value total	11,080
Held to maturity, gross unrealized losses total	13
Total held-to-maturity securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Held to maturity, fair value less than 12 months	14,848
Held-to-maturity, gross unrealized losses, less than 12 months	119
Held to maturity, fair value 12 months or longer	1,241
Held to maturity, gross unrealized losses 12 months or longer	70
Held to maturity, fair value total	16,089
Held to maturity, gross unrealized losses total	$ 189