Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) $ in Millions	Mar. 31, 2021 USD ($)
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	$ 9,172
Available for sale, under 1 year, fair value	9,202
Available for sale, 1 to 5 years, amortized cost	26,512
Available for sale, 1 to 5 years, fair value	26,740
Available for sale, 6 to 10 years, amortized cost	11,478
Available for sale, 6 to 10 years, fair value	11,535
Available for sale, over 10 years, amortized cost	12,817
Available for sale, over 10 years, fair value	13,035
Available for sale, amortized cost	59,979
Available for sale, fair value	60,512
Held to maturity, under 1 year, amortized cost	5,655
Held to maturity, under 1 year, fair value	5,704
Held to maturity, 1 to 5 years, amortized cost	1,854
Held to maturity, 1 to 5 years, fair value	1,883
Held to maturity, 6 to 10 years, amortized cost	6,008
Held to maturity, 6 to 10 years, fair value	5,942
Held to maturity, over 10 years, amortized cost	32,947
Held to maturity, over 10 years, fair value	33,424
Held to maturity, amortized cost	46,464
Held to maturity, fair value	46,953
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	3,211
Available for sale, under 1 year, fair value	3,219
Available for sale, 1 to 5 years, amortized cost	3,524
Available for sale, 1 to 5 years, fair value	3,513
Available for sale, 6 to 10 years, amortized cost	2,213
Available for sale, 6 to 10 years, fair value	2,205
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	8,948
Available for sale, fair value	8,937
Held to maturity, under 1 year, amortized cost	4,405
Held to maturity, under 1 year, fair value	4,444
Held to maturity, 1 to 5 years, amortized cost	1,104
Held to maturity, 1 to 5 years, fair value	1,126
Held to maturity, 6 to 10 years, amortized cost	1
Held to maturity, 6 to 10 years, fair value	1
Held to maturity, over 10 years, amortized cost	20
Held to maturity, over 10 years, fair value	20
Held to maturity, amortized cost	5,530
Held to maturity, fair value	5,591
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	109
Available for sale, under 1 year, fair value	114
Available for sale, 1 to 5 years, amortized cost	795
Available for sale, 1 to 5 years, fair value	808
Available for sale, 6 to 10 years, amortized cost	3,808
Available for sale, 6 to 10 years, fair value	3,830
Available for sale, over 10 years, amortized cost	9,469
Available for sale, over 10 years, fair value	9,673
Available for sale, amortized cost	14,181
Available for sale, fair value	14,425
Held to maturity, under 1 year, amortized cost	220
Held to maturity, under 1 year, fair value	228
Held to maturity, 1 to 5 years, amortized cost	350
Held to maturity, 1 to 5 years, fair value	357
Held to maturity, 6 to 10 years, amortized cost	5,104
Held to maturity, 6 to 10 years, fair value	5,031
Held to maturity, over 10 years, amortized cost	29,256
Held to maturity, over 10 years, fair value	29,621
Held to maturity, amortized cost	34,930
Held to maturity, fair value	35,237
Total U.S. Treasury and federal agencies
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	3,320
Available for sale, under 1 year, fair value	3,333
Available for sale, 1 to 5 years, amortized cost	4,319
Available for sale, 1 to 5 years, fair value	4,321
Available for sale, 6 to 10 years, amortized cost	6,021
Available for sale, 6 to 10 years, fair value	6,035
Available for sale, over 10 years, amortized cost	9,469
Available for sale, over 10 years, fair value	9,673
Available for sale, amortized cost	23,129
Available for sale, fair value	23,362
Held to maturity, under 1 year, amortized cost	4,625
Held to maturity, under 1 year, fair value	4,672
Held to maturity, 1 to 5 years, amortized cost	1,454
Held to maturity, 1 to 5 years, fair value	1,483
Held to maturity, 6 to 10 years, amortized cost	5,105
Held to maturity, 6 to 10 years, fair value	5,032
Held to maturity, over 10 years, amortized cost	29,276
Held to maturity, over 10 years, fair value	29,641
Held to maturity, amortized cost	40,460
Held to maturity, fair value	40,828
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	123
Available for sale, under 1 year, fair value	127
Available for sale, 1 to 5 years, amortized cost	54
Available for sale, 1 to 5 years, fair value	53
Available for sale, 6 to 10 years, amortized cost	0
Available for sale, 6 to 10 years, fair value	0
Available for sale, over 10 years, amortized cost	106
Available for sale, over 10 years, fair value	108
Available for sale, amortized cost	283
Available for sale, fair value	288
Held to maturity, under 1 year, amortized cost	364
Held to maturity, under 1 year, fair value	357
Held to maturity, 1 to 5 years, amortized cost	125
Held to maturity, 1 to 5 years, fair value	123
Held to maturity, 6 to 10 years, amortized cost	901
Held to maturity, 6 to 10 years, fair value	908
Held to maturity, over 10 years, amortized cost	3,355
Held to maturity, over 10 years, fair value	3,380
Held to maturity, amortized cost	4,745
Held to maturity, fair value	4,768
Asset-backed securities, credit cards
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	0
Available for sale, under 1 year, fair value	0
Available for sale, 1 to 5 years, amortized cost	0
Available for sale, 1 to 5 years, fair value	0
Available for sale, 6 to 10 years, amortized cost	90
Available for sale, 6 to 10 years, fair value	91
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	90
Available for sale, fair value	91
Asset-backed securities, collateralized loan obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	71
Available for sale, under 1 year, fair value	71
Available for sale, 1 to 5 years, amortized cost	961
Available for sale, 1 to 5 years, fair value	963
Available for sale, 6 to 10 years, amortized cost	1,398
Available for sale, 6 to 10 years, fair value	1,399
Available for sale, over 10 years, amortized cost	1,340
Available for sale, over 10 years, fair value	1,342
Available for sale, amortized cost	3,770
Available for sale, fair value	3,775
Non-agency CMBS and RMBS
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	0
Available for sale, under 1 year, fair value	0
Available for sale, 1 to 5 years, amortized cost	0
Available for sale, 1 to 5 years, fair value	0
Available for sale, 6 to 10 years, amortized cost	0
Available for sale, 6 to 10 years, fair value	0
Available for sale, over 10 years, amortized cost	70
Available for sale, over 10 years, fair value	71
Available for sale, amortized cost	70
Available for sale, fair value	71
Held to maturity, under 1 year, amortized cost	135
Held to maturity, under 1 year, fair value	147
Held to maturity, 1 to 5 years, amortized cost	253
Held to maturity, 1 to 5 years, fair value	255
Held to maturity, 6 to 10 years, amortized cost	2
Held to maturity, 6 to 10 years, fair value	2
Held to maturity, over 10 years, amortized cost	136
Held to maturity, over 10 years, fair value	153
Held to maturity, amortized cost	526
Held to maturity, fair value	557
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	194
Available for sale, under 1 year, fair value	198
Available for sale, 1 to 5 years, amortized cost	1,015
Available for sale, 1 to 5 years, fair value	1,016
Available for sale, 6 to 10 years, amortized cost	1,488
Available for sale, 6 to 10 years, fair value	1,490
Available for sale, over 10 years, amortized cost	1,516
Available for sale, over 10 years, fair value	1,521
Available for sale, amortized cost	4,213
Available for sale, fair value	4,225
Held to maturity, under 1 year, amortized cost	499
Held to maturity, under 1 year, fair value	504
Held to maturity, 1 to 5 years, amortized cost	378
Held to maturity, 1 to 5 years, fair value	378
Held to maturity, 6 to 10 years, amortized cost	903
Held to maturity, 6 to 10 years, fair value	910
Held to maturity, over 10 years, amortized cost	3,491
Held to maturity, over 10 years, fair value	3,533
Held to maturity, amortized cost	5,271
Held to maturity, fair value	5,325
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	276
Available for sale, under 1 year, fair value	277
Available for sale, 1 to 5 years, amortized cost	576
Available for sale, 1 to 5 years, fair value	578
Available for sale, 6 to 10 years, amortized cost	49
Available for sale, 6 to 10 years, fair value	50
Available for sale, over 10 years, amortized cost	1,120
Available for sale, over 10 years, fair value	1,127
Available for sale, amortized cost	2,021
Available for sale, fair value	2,032
Held to maturity, under 1 year, amortized cost	84
Held to maturity, under 1 year, fair value	81
Held to maturity, 1 to 5 years, amortized cost	22
Held to maturity, 1 to 5 years, fair value	22
Held to maturity, 6 to 10 years, amortized cost	0
Held to maturity, 6 to 10 years, fair value	0
Held to maturity, over 10 years, amortized cost	180
Held to maturity, over 10 years, fair value	250
Held to maturity, amortized cost	286
Held to maturity, fair value	353
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	299
Available for sale, under 1 year, fair value	299
Available for sale, 1 to 5 years, amortized cost	1,101
Available for sale, 1 to 5 years, fair value	1,101
Available for sale, 6 to 10 years, amortized cost	525
Available for sale, 6 to 10 years, fair value	526
Available for sale, over 10 years, amortized cost	371
Available for sale, over 10 years, fair value	371
Available for sale, amortized cost	2,296
Available for sale, fair value	2,297
Non-U.S. debt securities, government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	2,526
Available for sale, under 1 year, fair value	2,527
Available for sale, 1 to 5 years, amortized cost	6,736
Available for sale, 1 to 5 years, fair value	6,866
Available for sale, 6 to 10 years, amortized cost	453
Available for sale, 6 to 10 years, fair value	458
Available for sale, over 10 years, amortized cost	58
Available for sale, over 10 years, fair value	59
Available for sale, amortized cost	9,773
Available for sale, fair value	9,910
Held to maturity, under 1 year, amortized cost	246
Held to maturity, under 1 year, fair value	246
Held to maturity, 1 to 5 years, amortized cost	0
Held to maturity, 1 to 5 years, fair value	0
Held to maturity, 6 to 10 years, amortized cost	0
Held to maturity, 6 to 10 years, fair value	0
Held to maturity, over 10 years, amortized cost	0
Held to maturity, over 10 years, fair value	0
Held to maturity, amortized cost	246
Held to maturity, fair value	246
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	1,823
Available for sale, under 1 year, fair value	1,830
Available for sale, 1 to 5 years, amortized cost	9,370
Available for sale, 1 to 5 years, fair value	9,407
Available for sale, 6 to 10 years, amortized cost	2,375
Available for sale, 6 to 10 years, fair value	2,367
Available for sale, over 10 years, amortized cost	111
Available for sale, over 10 years, fair value	105
Available for sale, amortized cost	13,679
Available for sale, fair value	13,709
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	4,924
Available for sale, under 1 year, fair value	4,933
Available for sale, 1 to 5 years, amortized cost	17,783
Available for sale, 1 to 5 years, fair value	17,952
Available for sale, 6 to 10 years, amortized cost	3,402
Available for sale, 6 to 10 years, fair value	3,401
Available for sale, over 10 years, amortized cost	1,660
Available for sale, over 10 years, fair value	1,662
Available for sale, amortized cost	27,769
Available for sale, fair value	27,948
Held to maturity, under 1 year, amortized cost	330
Held to maturity, under 1 year, fair value	327
Held to maturity, 1 to 5 years, amortized cost	22
Held to maturity, 1 to 5 years, fair value	22
Held to maturity, 6 to 10 years, amortized cost	0
Held to maturity, 6 to 10 years, fair value	0
Held to maturity, over 10 years, amortized cost	180
Held to maturity, over 10 years, fair value	250
Held to maturity, amortized cost	532
Held to maturity, fair value	599
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	144
Available for sale, under 1 year, fair value	144
Available for sale, 1 to 5 years, amortized cost	609
Available for sale, 1 to 5 years, fair value	631
Available for sale, 6 to 10 years, amortized cost	506
Available for sale, 6 to 10 years, fair value	544
Available for sale, over 10 years, amortized cost	172
Available for sale, over 10 years, fair value	179
Available for sale, amortized cost	1,431
Available for sale, fair value	1,498
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	590
Available for sale, under 1 year, fair value	594
Available for sale, 1 to 5 years, amortized cost	2,786
Available for sale, 1 to 5 years, fair value	2,820
Available for sale, 6 to 10 years, amortized cost	61
Available for sale, 6 to 10 years, fair value	65
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	3,437
Available for sale, fair value	3,479
Total
Contractual Maturities Of Debt Investment Securities [Line Items]
Held to maturity, under 1 year, amortized cost	5,454
Held to maturity, under 1 year, fair value	5,503
Held to maturity, 1 to 5 years, amortized cost	1,854
Held to maturity, 1 to 5 years, fair value	1,883
Held to maturity, 6 to 10 years, amortized cost	6,008
Held to maturity, 6 to 10 years, fair value	5,942
Held to maturity, over 10 years, amortized cost	32,947
Held to maturity, over 10 years, fair value	33,424
Held to maturity, amortized cost	46,263
Held to maturity, fair value	46,752
Held-to-maturity under money market mutual fund liquidity facility
Contractual Maturities Of Debt Investment Securities [Line Items]
Held to maturity, under 1 year, amortized cost	201
Held to maturity, under 1 year, fair value	201
Held to maturity, 1 to 5 years, amortized cost	0
Held to maturity, 1 to 5 years, fair value	0
Held to maturity, 6 to 10 years, amortized cost	0
Held to maturity, 6 to 10 years, fair value	0
Held to maturity, over 10 years, amortized cost	0
Held to maturity, over 10 years, fair value	0
Held to maturity, amortized cost	201
Held to maturity, fair value	$ 201