Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) $ in Millions	Dec. 31, 2020 USD ($)
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	$ 7,612
Available for sale, under 1 year, fair value	7,644
Available for sale, 1 to 5 years, amortized cost	27,242
Available for sale, 1 to 5 years, fair value	27,656
Available for sale, 6 to 10 years, amortized cost	9,403
Available for sale, 6 to 10 years, fair value	9,632
Available for sale, over 10 years, amortized cost	13,730
Available for sale, over 10 years, fair value	14,116
Available for sale, amortized cost	57,987
Available for sale, fair value	59,048
Held to maturity, under 1 year, amortized cost	7,902
Held to maturity, under 1 year, fair value	7,946
Held to maturity, 1 to 5 years, amortized cost	3,421
Held to maturity, 1 to 5 years, fair value	3,478
Held to maturity, 6 to 10 years, amortized cost	5,724
Held to maturity, 6 to 10 years, fair value	5,860
Held to maturity, over 10 years, amortized cost	35,184
Held to maturity, over 10 years, fair value	36,023
Held to maturity, amortized cost	52,231
Held to maturity, fair value	53,307
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	1,648
Available for sale, under 1 year, fair value	1,661
Available for sale, 1 to 5 years, amortized cost	2,758
Available for sale, 1 to 5 years, fair value	2,771
Available for sale, 6 to 10 years, amortized cost	2,047
Available for sale, 6 to 10 years, fair value	2,143
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	6,453
Available for sale, fair value	6,575
Held to maturity, under 1 year, amortized cost	3,480
Held to maturity, under 1 year, fair value	3,512
Held to maturity, 1 to 5 years, amortized cost	2,555
Held to maturity, 1 to 5 years, fair value	2,607
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	22
Held to maturity, over 10 years, fair value	21
Held to maturity, amortized cost	6,057
Held to maturity, fair value	6,140
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	121
Available for sale, under 1 year, fair value	127
Available for sale, 1 to 5 years, amortized cost	603
Available for sale, 1 to 5 years, fair value	619
Available for sale, 6 to 10 years, amortized cost	2,800
Available for sale, 6 to 10 years, fair value	2,828
Available for sale, over 10 years, amortized cost	10,367
Available for sale, over 10 years, fair value	10,731
Available for sale, amortized cost	13,891
Available for sale, fair value	14,305
Held to maturity, under 1 year, amortized cost	204
Held to maturity, under 1 year, fair value	211
Held to maturity, 1 to 5 years, amortized cost	423
Held to maturity, 1 to 5 years, fair value	430
Held to maturity, 6 to 10 years, amortized cost	5,036
Held to maturity, 6 to 10 years, fair value	5,174
Held to maturity, over 10 years, amortized cost	31,220
Held to maturity, over 10 years, fair value	31,956
Held to maturity, amortized cost	36,883
Held to maturity, fair value	37,771
Total U.S. Treasury and federal agencies
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	1,769
Available for sale, under 1 year, fair value	1,788
Available for sale, 1 to 5 years, amortized cost	3,361
Available for sale, 1 to 5 years, fair value	3,390
Available for sale, 6 to 10 years, amortized cost	4,847
Available for sale, 6 to 10 years, fair value	4,971
Available for sale, over 10 years, amortized cost	10,367
Available for sale, over 10 years, fair value	10,731
Available for sale, amortized cost	20,344
Available for sale, fair value	20,880
Held to maturity, under 1 year, amortized cost	3,684
Held to maturity, under 1 year, fair value	3,723
Held to maturity, 1 to 5 years, amortized cost	2,978
Held to maturity, 1 to 5 years, fair value	3,037
Held to maturity, 6 to 10 years, amortized cost	5,036
Held to maturity, 6 to 10 years, fair value	5,174
Held to maturity, over 10 years, amortized cost	31,242
Held to maturity, over 10 years, fair value	31,977
Held to maturity, amortized cost	42,940
Held to maturity, fair value	43,911
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	113
Available for sale, under 1 year, fair value	115
Available for sale, 1 to 5 years, amortized cost	90
Available for sale, 1 to 5 years, fair value	90
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	110
Available for sale, over 10 years, fair value	109
Available for sale, amortized cost	313
Available for sale, fair value	314
Held to maturity, under 1 year, amortized cost	350
Held to maturity, under 1 year, fair value	343
Held to maturity, 1 to 5 years, amortized cost	155
Held to maturity, 1 to 5 years, fair value	152
Held to maturity, 6 to 10 years, amortized cost	667
Held to maturity, 6 to 10 years, fair value	665
Held to maturity, over 10 years, amortized cost	3,602
Held to maturity, over 10 years, fair value	3,622
Held to maturity, amortized cost	4,774
Held to maturity, fair value	4,782
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	90
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	90
Asset-backed securities, collateralized loan obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	76
Available for sale, under 1 year, fair value	76
Available for sale, 1 to 5 years, amortized cost	1,080
Available for sale, 1 to 5 years, fair value	1,077
Available for sale, 6 to 10 years, amortized cost	838
Available for sale, 6 to 10 years, fair value	838
Available for sale, over 10 years, amortized cost	975
Available for sale, over 10 years, fair value	975
Available for sale, amortized cost	2,969
Available for sale, fair value	2,966
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	189
Available for sale, under 1 year, fair value	191
Available for sale, 1 to 5 years, amortized cost	1,170
Available for sale, 1 to 5 years, fair value	1,167
Available for sale, 6 to 10 years, amortized cost	928
Available for sale, 6 to 10 years, fair value	928
Available for sale, over 10 years, amortized cost	1,085
Available for sale, over 10 years, fair value	1,084
Available for sale, amortized cost	3,372
Available for sale, fair value	3,370
Held to maturity, under 1 year, amortized cost	350
Held to maturity, under 1 year, fair value	343
Held to maturity, 1 to 5 years, amortized cost	155
Held to maturity, 1 to 5 years, fair value	152
Held to maturity, 6 to 10 years, amortized cost	667
Held to maturity, 6 to 10 years, fair value	665
Held to maturity, over 10 years, amortized cost	3,602
Held to maturity, over 10 years, fair value	3,622
Held to maturity, amortized cost	4,774
Held to maturity, fair value	4,782
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	260
Available for sale, under 1 year, fair value	260
Available for sale, 1 to 5 years, amortized cost	527
Available for sale, 1 to 5 years, fair value	527
Available for sale, 6 to 10 years, amortized cost	116
Available for sale, 6 to 10 years, fair value	116
Available for sale, over 10 years, amortized cost	1,091
Available for sale, over 10 years, fair value	1,093
Available for sale, amortized cost	1,994
Available for sale, fair value	1,996
Held to maturity, under 1 year, amortized cost	87
Held to maturity, under 1 year, fair value	84
Held to maturity, 1 to 5 years, amortized cost	23
Held to maturity, 1 to 5 years, fair value	23
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	193
Held to maturity, over 10 years, fair value	260
Held to maturity, amortized cost	303
Held to maturity, fair value	367
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	337
Available for sale, under 1 year, fair value	337
Available for sale, 1 to 5 years, amortized cost	1,250
Available for sale, 1 to 5 years, fair value	1,247
Available for sale, 6 to 10 years, amortized cost	272
Available for sale, 6 to 10 years, fair value	272
Available for sale, over 10 years, amortized cost	435
Available for sale, over 10 years, fair value	435
Available for sale, amortized cost	2,294
Available for sale, fair value	2,291
Non-U.S. debt securities, government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	3,149
Available for sale, under 1 year, fair value	3,151
Available for sale, 1 to 5 years, amortized cost	7,976
Available for sale, 1 to 5 years, fair value	8,151
Available for sale, 6 to 10 years, amortized cost	919
Available for sale, 6 to 10 years, fair value	939
Available for sale, over 10 years, amortized cost	293
Available for sale, over 10 years, fair value	298
Available for sale, amortized cost	12,337
Available for sale, fair value	12,539
Held to maturity, under 1 year, amortized cost	342
Held to maturity, under 1 year, fair value	342
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	342
Held to maturity, fair value	342
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	1,323
Available for sale, under 1 year, fair value	1,329
Available for sale, 1 to 5 years, amortized cost	9,520
Available for sale, 1 to 5 years, fair value	9,652
Available for sale, 6 to 10 years, amortized cost	1,718
Available for sale, 6 to 10 years, fair value	1,752
Available for sale, over 10 years, amortized cost	168
Available for sale, over 10 years, fair value	170
Available for sale, amortized cost	12,729
Available for sale, fair value	12,903
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	5,069
Available for sale, under 1 year, fair value	5,077
Available for sale, 1 to 5 years, amortized cost	19,273
Available for sale, 1 to 5 years, fair value	19,577
Available for sale, 6 to 10 years, amortized cost	3,025
Available for sale, 6 to 10 years, fair value	3,079
Available for sale, over 10 years, amortized cost	1,987
Available for sale, over 10 years, fair value	1,996
Available for sale, amortized cost	29,354
Available for sale, fair value	29,729
Held to maturity, under 1 year, amortized cost	429
Held to maturity, under 1 year, fair value	426
Held to maturity, 1 to 5 years, amortized cost	23
Held to maturity, 1 to 5 years, fair value	23
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	193
Held to maturity, over 10 years, fair value	260
Held to maturity, amortized cost	645
Held to maturity, fair value	709
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	136
Available for sale, under 1 year, fair value	136
Available for sale, 1 to 5 years, amortized cost	605
Available for sale, 1 to 5 years, fair value	626
Available for sale, 6 to 10 years, amortized cost	514
Available for sale, 6 to 10 years, fair value	559
Available for sale, over 10 years, amortized cost	215
Available for sale, over 10 years, fair value	227
Available for sale, amortized cost	1,470
Available for sale, fair value	1,548
Collateralized mortgage obligations
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	76
Available for sale, over 10 years, fair value	78
Available for sale, amortized cost	76
Available for sale, fair value	78
Held to maturity, under 1 year, amortized cost	139
Held to maturity, under 1 year, fair value	150
Held to maturity, 1 to 5 years, amortized cost	265
Held to maturity, 1 to 5 years, fair value	266
Held to maturity, 6 to 10 years, amortized cost	21
Held to maturity, 6 to 10 years, fair value	21
Held to maturity, over 10 years, amortized cost	147
Held to maturity, over 10 years, fair value	164
Held to maturity, amortized cost	572
Held to maturity, fair value	601
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	449
Available for sale, under 1 year, fair value	452
Available for sale, 1 to 5 years, amortized cost	2,833
Available for sale, 1 to 5 years, fair value	2,896
Available for sale, 6 to 10 years, amortized cost	89
Available for sale, 6 to 10 years, fair value	95
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	3,371
Available for sale, fair value	3,443
Total
Contractual Maturities Of Debt Investment Securities [Line Items]
Held to maturity, under 1 year, amortized cost	4,602
Held to maturity, under 1 year, fair value	4,642
Held to maturity, 1 to 5 years, amortized cost	3,421
Held to maturity, 1 to 5 years, fair value	3,478
Held to maturity, 6 to 10 years, amortized cost	5,724
Held to maturity, 6 to 10 years, fair value	5,860
Held to maturity, over 10 years, amortized cost	35,184
Held to maturity, over 10 years, fair value	36,023
Held to maturity, amortized cost	48,931
Held to maturity, fair value	50,003
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	3,300
Held to maturity, under 1 year, fair value	3,304
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	3,300
Held to maturity, fair value	$ 3,304