Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) $ in Millions	Sep. 30, 2021 USD ($)
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	$ 10,327
Available for sale, under 1 year, fair value	10,354
Available for sale, 1 to 5 years, amortized cost	33,436
Available for sale, 1 to 5 years, fair value	33,557
Available for sale, 6 to 10 years, amortized cost	13,336
Available for sale, 6 to 10 years, fair value	13,413
Available for sale, over 10 years, amortized cost	12,808
Available for sale, over 10 years, fair value	12,955
Available for sale, amortized cost	69,907
Available for sale, fair value	70,279
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	2,112
Available for sale, under 1 year, fair value	2,114
Available for sale, 1 to 5 years, amortized cost	11,214
Available for sale, 1 to 5 years, fair value	11,169
Available for sale, 6 to 10 years, amortized cost	1,046
Available for sale, 6 to 10 years, fair value	1,056
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	14,372
Available for sale, fair value	14,339
Held to maturity, under 1 year, amortized cost	2,387
Held to maturity, under 1 year, fair value	2,403
Held to maturity, 1 to 5 years, amortized cost	304
Held to maturity, 1 to 5 years, fair value	309
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	18
Held to maturity, over 10 years, fair value	19
Held to maturity, amortized cost	2,709
Held to maturity, fair value	2,731
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	83
Available for sale, under 1 year, fair value	87
Available for sale, 1 to 5 years, amortized cost	845
Available for sale, 1 to 5 years, fair value	855
Available for sale, 6 to 10 years, amortized cost	6,227
Available for sale, 6 to 10 years, fair value	6,248
Available for sale, over 10 years, amortized cost	8,896
Available for sale, over 10 years, fair value	9,033
Available for sale, amortized cost	16,051
Available for sale, fair value	16,223
Held to maturity, under 1 year, amortized cost	171
Held to maturity, under 1 year, fair value	177
Held to maturity, 1 to 5 years, amortized cost	285
Held to maturity, 1 to 5 years, fair value	290
Held to maturity, 6 to 10 years, amortized cost	4,528
Held to maturity, 6 to 10 years, fair value	4,509
Held to maturity, over 10 years, amortized cost	28,541
Held to maturity, over 10 years, fair value	28,765
Held to maturity, amortized cost	33,525
Held to maturity, fair value	33,741
Total U.S. Treasury and federal agencies
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	2,195
Available for sale, under 1 year, fair value	2,201
Available for sale, 1 to 5 years, amortized cost	12,059
Available for sale, 1 to 5 years, fair value	12,024
Available for sale, 6 to 10 years, amortized cost	7,273
Available for sale, 6 to 10 years, fair value	7,304
Available for sale, over 10 years, amortized cost	8,896
Available for sale, over 10 years, fair value	9,033
Available for sale, amortized cost	30,423
Available for sale, fair value	30,562
Held to maturity, under 1 year, amortized cost	2,558
Held to maturity, under 1 year, fair value	2,580
Held to maturity, 1 to 5 years, amortized cost	589
Held to maturity, 1 to 5 years, fair value	599
Held to maturity, 6 to 10 years, amortized cost	4,528
Held to maturity, 6 to 10 years, fair value	4,509
Held to maturity, over 10 years, amortized cost	28,559
Held to maturity, over 10 years, fair value	28,784
Held to maturity, amortized cost	36,234
Held to maturity, fair value	36,472
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	212
Available for sale, under 1 year, fair value	213
Available for sale, 1 to 5 years, amortized cost	540
Available for sale, 1 to 5 years, fair value	543
Available for sale, 6 to 10 years, amortized cost	40
Available for sale, 6 to 10 years, fair value	40
Available for sale, over 10 years, amortized cost	1,338
Available for sale, over 10 years, fair value	1,345
Available for sale, amortized cost	2,130
Available for sale, fair value	2,141
Held to maturity, under 1 year, amortized cost	38
Held to maturity, under 1 year, fair value	37
Held to maturity, 1 to 5 years, amortized cost	18
Held to maturity, 1 to 5 years, fair value	18
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	153
Held to maturity, over 10 years, fair value	217
Held to maturity, amortized cost	209
Held to maturity, fair value	272
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	271
Available for sale, under 1 year, fair value	271
Available for sale, 1 to 5 years, amortized cost	1,286
Available for sale, 1 to 5 years, fair value	1,287
Available for sale, 6 to 10 years, amortized cost	415
Available for sale, 6 to 10 years, fair value	415
Available for sale, over 10 years, amortized cost	393
Available for sale, over 10 years, fair value	392
Available for sale, amortized cost	2,365
Available for sale, fair value	2,365
Non-U.S. sovereign, supranational and non-U.S. agency
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	5,828
Available for sale, under 1 year, fair value	5,835
Available for sale, 1 to 5 years, amortized cost	13,987
Available for sale, 1 to 5 years, fair value	14,081
Available for sale, 6 to 10 years, amortized cost	2,917
Available for sale, 6 to 10 years, fair value	2,923
Available for sale, over 10 years, amortized cost	15
Available for sale, over 10 years, fair value	15
Available for sale, amortized cost	22,747
Available for sale, fair value	22,854
Held to maturity, under 1 year, amortized cost	275
Held to maturity, under 1 year, fair value	275
Held to maturity, 1 to 5 years, amortized cost	1,232
Held to maturity, 1 to 5 years, fair value	1,229
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	0
Held to maturity, over 10 years, fair value	0
Held to maturity, amortized cost	1,508
Held to maturity, fair value	1,505
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	786
Available for sale, under 1 year, fair value	790
Available for sale, 1 to 5 years, amortized cost	2,077
Available for sale, 1 to 5 years, fair value	2,089
Available for sale, 6 to 10 years, amortized cost	375
Available for sale, 6 to 10 years, fair value	371
Available for sale, over 10 years, amortized cost	56
Available for sale, over 10 years, fair value	56
Available for sale, amortized cost	3,294
Available for sale, fair value	3,306
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	7,097
Available for sale, under 1 year, fair value	7,109
Available for sale, 1 to 5 years, amortized cost	17,890
Available for sale, 1 to 5 years, fair value	18,000
Available for sale, 6 to 10 years, amortized cost	3,747
Available for sale, 6 to 10 years, fair value	3,749
Available for sale, over 10 years, amortized cost	1,802
Available for sale, over 10 years, fair value	1,808
Available for sale, amortized cost	30,536
Available for sale, fair value	30,666
Held to maturity, under 1 year, amortized cost	313
Held to maturity, under 1 year, fair value	312
Held to maturity, 1 to 5 years, amortized cost	1,250
Held to maturity, 1 to 5 years, fair value	1,247
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	153
Held to maturity, over 10 years, fair value	217
Held to maturity, amortized cost	1,717
Held to maturity, fair value	1,777
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	129
Available for sale, under 1 year, fair value	131
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	99
Available for sale, over 10 years, fair value	100
Available for sale, amortized cost	228
Available for sale, fair value	231
Held to maturity, under 1 year, amortized cost	349
Held to maturity, under 1 year, fair value	343
Held to maturity, 1 to 5 years, amortized cost	110
Held to maturity, 1 to 5 years, fair value	109
Held to maturity, 6 to 10 years, amortized cost	1,071
Held to maturity, 6 to 10 years, fair value	1,088
Held to maturity, over 10 years, amortized cost	3,487
Held to maturity, over 10 years, fair value	3,528
Held to maturity, amortized cost	5,017
Held to maturity, fair value	5,068
Asset-backed securities, collateralized loan obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	29
Available for sale, under 1 year, fair value	30
Available for sale, 1 to 5 years, amortized cost	760
Available for sale, 1 to 5 years, fair value	761
Available for sale, 6 to 10 years, amortized cost	1,656
Available for sale, 6 to 10 years, fair value	1,656
Available for sale, over 10 years, amortized cost	1,848
Available for sale, over 10 years, fair value	1,849
Available for sale, amortized cost	4,293
Available for sale, fair value	4,296
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	58
Available for sale, over 10 years, fair value	59
Available for sale, amortized cost	58
Available for sale, fair value	59
Held to maturity, under 1 year, amortized cost	127
Held to maturity, under 1 year, fair value	140
Held to maturity, 1 to 5 years, amortized cost	158
Held to maturity, 1 to 5 years, fair value	160
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	93
Held to maturity, over 10 years, fair value	109
Held to maturity, amortized cost	380
Held to maturity, fair value	411
Asset-backed securities, other
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	92
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	92
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	158
Available for sale, under 1 year, fair value	161
Available for sale, 1 to 5 years, amortized cost	760
Available for sale, 1 to 5 years, fair value	761
Available for sale, 6 to 10 years, amortized cost	1,746
Available for sale, 6 to 10 years, fair value	1,748
Available for sale, over 10 years, amortized cost	2,005
Available for sale, over 10 years, fair value	2,008
Available for sale, amortized cost	4,669
Available for sale, fair value	4,678
Held to maturity, under 1 year, amortized cost	476
Held to maturity, under 1 year, fair value	483
Held to maturity, 1 to 5 years, amortized cost	268
Held to maturity, 1 to 5 years, fair value	269
Held to maturity, 6 to 10 years, amortized cost	1,073
Held to maturity, 6 to 10 years, fair value	1,090
Held to maturity, over 10 years, amortized cost	3,580
Held to maturity, over 10 years, fair value	3,637
Held to maturity, amortized cost	5,397
Held to maturity, fair value	5,479
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	159
Available for sale, under 1 year, fair value	160
Available for sale, 1 to 5 years, amortized cost	544
Available for sale, 1 to 5 years, fair value	563
Available for sale, 6 to 10 years, amortized cost	528
Available for sale, 6 to 10 years, fair value	567
Available for sale, over 10 years, amortized cost	105
Available for sale, over 10 years, fair value	106
Available for sale, amortized cost	1,336
Available for sale, fair value	1,396
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	718
Available for sale, under 1 year, fair value	723
Available for sale, 1 to 5 years, amortized cost	2,183
Available for sale, 1 to 5 years, fair value	2,209
Available for sale, 6 to 10 years, amortized cost	42
Available for sale, 6 to 10 years, fair value	45
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	2,943
Available for sale, fair value	2,977
Total
Contractual Maturities Of Debt Investment Securities [Line Items]
Held to maturity, under 1 year, amortized cost	3,347
Held to maturity, under 1 year, fair value	3,375
Held to maturity, 1 to 5 years, amortized cost	2,107
Held to maturity, 1 to 5 years, fair value	2,115
Held to maturity, 6 to 10 years, amortized cost	5,602
Held to maturity, 6 to 10 years, fair value	5,600
Held to maturity, over 10 years, amortized cost	32,292
Held to maturity, over 10 years, fair value	32,638
Held to maturity, amortized cost	43,348
Held to maturity, fair value	$ 43,728