Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) $ in Millions	Jun. 30, 2020 USD ($)
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	$ 9,477
Available for sale, under 1 year, fair value	9,504
Available for sale, 1 to 5 years, amortized cost	22,230
Available for sale, 1 to 5 years, fair value	22,573
Available for sale, 6 to 10 years, amortized cost	8,800
Available for sale, 6 to 10 years, fair value	9,014
Available for sale, over 10 years, amortized cost	14,637
Available for sale, over 10 years, fair value	15,140
Available for sale, amortized cost	55,144
Available for sale, fair value	56,231
Held to maturity, under 1 year, amortized cost	15,650
Held to maturity, under 1 year, fair value	15,694
Held to maturity, 1 to 5 years, amortized cost	5,886
Held to maturity, 1 to 5 years, fair value	6,006
Held to maturity, 6 to 10 years, amortized cost	4,268
Held to maturity, 6 to 10 years, fair value	4,434
Held to maturity, over 10 years, amortized cost	27,305
Held to maturity, over 10 years, fair value	28,197
Held to maturity, amortized cost	53,109
Held to maturity, fair value	54,331
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	1,560
Available for sale, under 1 year, fair value	1,569
Available for sale, 1 to 5 years, amortized cost	2,022
Available for sale, 1 to 5 years, fair value	2,057
Available for sale, 6 to 10 years, amortized cost	2,049
Available for sale, 6 to 10 years, fair value	2,178
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	5,631
Available for sale, fair value	5,804
Held to maturity, under 1 year, amortized cost	3,310
Held to maturity, under 1 year, fair value	3,332
Held to maturity, 1 to 5 years, amortized cost	4,840
Held to maturity, 1 to 5 years, fair value	4,956
Held to maturity, 6 to 10 years, amortized cost	5
Held to maturity, 6 to 10 years, fair value	5
Held to maturity, over 10 years, amortized cost	24
Held to maturity, over 10 years, fair value	24
Held to maturity, amortized cost	8,179
Held to maturity, fair value	8,317
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	199
Available for sale, under 1 year, fair value	206
Available for sale, 1 to 5 years, amortized cost	706
Available for sale, 1 to 5 years, fair value	726
Available for sale, 6 to 10 years, amortized cost	2,639
Available for sale, 6 to 10 years, fair value	2,672
Available for sale, over 10 years, amortized cost	12,574
Available for sale, over 10 years, fair value	13,072
Available for sale, amortized cost	16,118
Available for sale, fair value	16,676
Held to maturity, under 1 year, amortized cost	61
Held to maturity, under 1 year, fair value	63
Held to maturity, 1 to 5 years, amortized cost	545
Held to maturity, 1 to 5 years, fair value	557
Held to maturity, 6 to 10 years, amortized cost	3,716
Held to maturity, 6 to 10 years, fair value	3,898
Held to maturity, over 10 years, amortized cost	23,882
Held to maturity, over 10 years, fair value	24,758
Held to maturity, amortized cost	28,204
Held to maturity, fair value	29,276
Total U.S. Treasury and federal agencies
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	1,759
Available for sale, under 1 year, fair value	1,775
Available for sale, 1 to 5 years, amortized cost	2,728
Available for sale, 1 to 5 years, fair value	2,783
Available for sale, 6 to 10 years, amortized cost	4,688
Available for sale, 6 to 10 years, fair value	4,850
Available for sale, over 10 years, amortized cost	12,574
Available for sale, over 10 years, fair value	13,072
Available for sale, amortized cost	21,749
Available for sale, fair value	22,480
Held to maturity, under 1 year, amortized cost	3,371
Held to maturity, under 1 year, fair value	3,395
Held to maturity, 1 to 5 years, amortized cost	5,385
Held to maturity, 1 to 5 years, fair value	5,513
Held to maturity, 6 to 10 years, amortized cost	3,721
Held to maturity, 6 to 10 years, fair value	3,903
Held to maturity, over 10 years, amortized cost	23,906
Held to maturity, over 10 years, fair value	24,782
Held to maturity, amortized cost	36,383
Held to maturity, fair value	37,593
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	163
Available for sale, under 1 year, fair value	164
Available for sale, 1 to 5 years, amortized cost	127
Available for sale, 1 to 5 years, fair value	126
Available for sale, 6 to 10 years, amortized cost	2
Available for sale, 6 to 10 years, fair value	2
Available for sale, over 10 years, amortized cost	117
Available for sale, over 10 years, fair value	112
Available for sale, amortized cost	409
Available for sale, fair value	404
Held to maturity, under 1 year, amortized cost	359
Held to maturity, under 1 year, fair value	343
Held to maturity, 1 to 5 years, amortized cost	200
Held to maturity, 1 to 5 years, fair value	193
Held to maturity, 6 to 10 years, amortized cost	539
Held to maturity, 6 to 10 years, fair value	523
Held to maturity, over 10 years, amortized cost	3,050
Held to maturity, over 10 years, fair value	2,993
Held to maturity, amortized cost	4,148
Held to maturity, fair value	4,052
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	31
Available for sale, under 1 year, fair value	29
Available for sale, 1 to 5 years, amortized cost	978
Available for sale, 1 to 5 years, fair value	964
Available for sale, 6 to 10 years, amortized cost	823
Available for sale, 6 to 10 years, fair value	811
Available for sale, over 10 years, amortized cost	117
Available for sale, over 10 years, fair value	115
Available for sale, amortized cost	1,949
Available for sale, fair value	1,919
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	193
Available for sale, 1 to 5 years, amortized cost	1,105
Available for sale, 1 to 5 years, fair value	1,090
Available for sale, 6 to 10 years, amortized cost	915
Available for sale, 6 to 10 years, fair value	903
Available for sale, over 10 years, amortized cost	234
Available for sale, over 10 years, fair value	227
Available for sale, amortized cost	2,448
Available for sale, fair value	2,413
Held to maturity, under 1 year, amortized cost	359
Held to maturity, under 1 year, fair value	343
Held to maturity, 1 to 5 years, amortized cost	200
Held to maturity, 1 to 5 years, fair value	193
Held to maturity, 6 to 10 years, amortized cost	539
Held to maturity, 6 to 10 years, fair value	523
Held to maturity, over 10 years, amortized cost	3,050
Held to maturity, over 10 years, fair value	2,993
Held to maturity, amortized cost	4,148
Held to maturity, fair value	4,052
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	252
Available for sale, under 1 year, fair value	251
Available for sale, 1 to 5 years, amortized cost	550
Available for sale, 1 to 5 years, fair value	546
Available for sale, 6 to 10 years, amortized cost	130
Available for sale, 6 to 10 years, fair value	129
Available for sale, over 10 years, amortized cost	782
Available for sale, over 10 years, fair value	780
Available for sale, amortized cost	1,714
Available for sale, fair value	1,706
Held to maturity, under 1 year, amortized cost	117
Held to maturity, under 1 year, fair value	112
Held to maturity, 1 to 5 years, amortized cost	27
Held to maturity, 1 to 5 years, fair value	27
Held to maturity, 6 to 10 years, amortized cost	3
Held to maturity, 6 to 10 years, fair value	3
Held to maturity, over 10 years, amortized cost	192
Held to maturity, over 10 years, fair value	250
Held to maturity, amortized cost	339
Held to maturity, fair value	392
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	272
Available for sale, under 1 year, fair value	270
Available for sale, 1 to 5 years, amortized cost	984
Available for sale, 1 to 5 years, fair value	977
Available for sale, 6 to 10 years, amortized cost	318
Available for sale, 6 to 10 years, fair value	315
Available for sale, over 10 years, amortized cost	332
Available for sale, over 10 years, fair value	329
Available for sale, amortized cost	1,906
Available for sale, fair value	1,891
Non-U.S. debt securities, government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	4,690
Available for sale, under 1 year, fair value	4,694
Available for sale, 1 to 5 years, amortized cost	7,339
Available for sale, 1 to 5 years, fair value	7,488
Available for sale, 6 to 10 years, amortized cost	689
Available for sale, 6 to 10 years, fair value	693
Available for sale, over 10 years, amortized cost	246
Available for sale, over 10 years, fair value	244
Available for sale, amortized cost	12,964
Available for sale, fair value	13,119
Held to maturity, under 1 year, amortized cost	393
Held to maturity, under 1 year, fair value	393
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	393
Held to maturity, fair value	393
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	1,446
Available for sale, under 1 year, fair value	1,452
Available for sale, 1 to 5 years, amortized cost	6,968
Available for sale, 1 to 5 years, fair value	7,068
Available for sale, 6 to 10 years, amortized cost	1,431
Available for sale, 6 to 10 years, fair value	1,451
Available for sale, over 10 years, amortized cost	90
Available for sale, over 10 years, fair value	91
Available for sale, amortized cost	9,935
Available for sale, fair value	10,062
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	6,660
Available for sale, under 1 year, fair value	6,667
Available for sale, 1 to 5 years, amortized cost	15,841
Available for sale, 1 to 5 years, fair value	16,079
Available for sale, 6 to 10 years, amortized cost	2,568
Available for sale, 6 to 10 years, fair value	2,588
Available for sale, over 10 years, amortized cost	1,450
Available for sale, over 10 years, fair value	1,444
Available for sale, amortized cost	26,519
Available for sale, fair value	26,778
Held to maturity, under 1 year, amortized cost	510
Held to maturity, under 1 year, fair value	505
Held to maturity, 1 to 5 years, amortized cost	27
Held to maturity, 1 to 5 years, fair value	27
Held to maturity, 6 to 10 years, amortized cost	3
Held to maturity, 6 to 10 years, fair value	3
Held to maturity, over 10 years, amortized cost	192
Held to maturity, over 10 years, fair value	250
Held to maturity, amortized cost	732
Held to maturity, fair value	785
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	169
Available for sale, under 1 year, fair value	169
Available for sale, 1 to 5 years, amortized cost	669
Available for sale, 1 to 5 years, fair value	683
Available for sale, 6 to 10 years, amortized cost	526
Available for sale, 6 to 10 years, fair value	564
Available for sale, over 10 years, amortized cost	290
Available for sale, over 10 years, fair value	307
Available for sale, amortized cost	1,654
Available for sale, fair value	1,723
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	89
Available for sale, over 10 years, fair value	90
Available for sale, amortized cost	89
Available for sale, fair value	90
Held to maturity, under 1 year, amortized cost	149
Held to maturity, under 1 year, fair value	157
Held to maturity, 1 to 5 years, amortized cost	274
Held to maturity, 1 to 5 years, fair value	273
Held to maturity, 6 to 10 years, amortized cost	5
Held to maturity, 6 to 10 years, fair value	5
Held to maturity, over 10 years, amortized cost	157
Held to maturity, over 10 years, fair value	172
Held to maturity, amortized cost	585
Held to maturity, fair value	607
Total
Contractual Maturities Of Debt Investment Securities [Line Items]
Held to maturity, under 1 year, amortized cost	4,389
Held to maturity, under 1 year, fair value	4,400
Held to maturity, 1 to 5 years, amortized cost	5,886
Held to maturity, 1 to 5 years, fair value	6,006
Held to maturity, 6 to 10 years, amortized cost	4,268
Held to maturity, 6 to 10 years, fair value	4,434
Held to maturity, over 10 years, amortized cost	27,305
Held to maturity, over 10 years, fair value	28,197
Held to maturity, amortized cost	41,848
Held to maturity, fair value	43,037
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	695
Available for sale, under 1 year, fair value	700
Available for sale, 1 to 5 years, amortized cost	1,887
Available for sale, 1 to 5 years, fair value	1,938
Available for sale, 6 to 10 years, amortized cost	103
Available for sale, 6 to 10 years, fair value	109
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	2,685
Available for sale, fair value	2,747
Money Market Liquidity Facility
Contractual Maturities Of Debt Investment Securities [Line Items]
Held to maturity, under 1 year, amortized cost	11,261
Held to maturity, under 1 year, fair value	11,294
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	11,261
Held to maturity, fair value	$ 11,294