Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) $ in Millions	Mar. 31, 2020 USD ($)
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	$ 8,467
Available for sale, under 1 year, fair value	8,477
Available for sale, 1 to 5 years, amortized cost	21,813
Available for sale, 1 to 5 years, fair value	21,910
Available for sale, 6 to 10 years, amortized cost	8,705
Available for sale, 6 to 10 years, fair value	8,784
Available for sale, over 10 years, amortized cost	16,214
Available for sale, over 10 years, fair value	16,672
Available for sale, amortized cost	55,199
Available for sale, fair value	55,843
Held to maturity, under 1 year, amortized cost	30,824
Held to maturity, under 1 year, fair value	30,836
Held to maturity, 1 to 5 years, amortized cost	6,572
Held to maturity, 1 to 5 years, fair value	6,731
Held to maturity, 6 to 10 years, amortized cost	3,636
Held to maturity, 6 to 10 years, fair value	3,752
Held to maturity, over 10 years, amortized cost	26,930
Held to maturity, over 10 years, fair value	27,690
Held to maturity, amortized cost	67,962
Held to maturity, fair value	69,009
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	1,060
Available for sale, under 1 year, fair value	1,075
Available for sale, 1 to 5 years, amortized cost	1,873
Available for sale, 1 to 5 years, fair value	1,907
Available for sale, 6 to 10 years, amortized cost	2,050
Available for sale, 6 to 10 years, fair value	2,168
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	4,983
Available for sale, fair value	5,150
Held to maturity, under 1 year, amortized cost	3,609
Held to maturity, under 1 year, fair value	3,633
Held to maturity, 1 to 5 years, amortized cost	5,628
Held to maturity, 1 to 5 years, fair value	5,775
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	26
Held to maturity, over 10 years, fair value	26
Held to maturity, amortized cost	9,268
Held to maturity, fair value	9,439
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	111
Available for sale, under 1 year, fair value	116
Available for sale, 1 to 5 years, amortized cost	882
Available for sale, 1 to 5 years, fair value	900
Available for sale, 6 to 10 years, amortized cost	2,825
Available for sale, 6 to 10 years, fair value	2,831
Available for sale, over 10 years, amortized cost	14,024
Available for sale, over 10 years, fair value	14,517
Available for sale, amortized cost	17,842
Available for sale, fair value	18,364
Held to maturity, under 1 year, amortized cost	6
Held to maturity, under 1 year, fair value	6
Held to maturity, 1 to 5 years, amortized cost	438
Held to maturity, 1 to 5 years, fair value	451
Held to maturity, 6 to 10 years, amortized cost	3,098
Held to maturity, 6 to 10 years, fair value	3,238
Held to maturity, over 10 years, amortized cost	23,071
Held to maturity, over 10 years, fair value	23,881
Held to maturity, amortized cost	26,613
Held to maturity, fair value	27,576
Total U.S. Treasury and federal agencies
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	1,171
Available for sale, under 1 year, fair value	1,191
Available for sale, 1 to 5 years, amortized cost	2,755
Available for sale, 1 to 5 years, fair value	2,807
Available for sale, 6 to 10 years, amortized cost	4,875
Available for sale, 6 to 10 years, fair value	4,999
Available for sale, over 10 years, amortized cost	14,024
Available for sale, over 10 years, fair value	14,517
Available for sale, amortized cost	22,825
Available for sale, fair value	23,514
Held to maturity, under 1 year, amortized cost	3,615
Held to maturity, under 1 year, fair value	3,639
Held to maturity, 1 to 5 years, amortized cost	6,066
Held to maturity, 1 to 5 years, fair value	6,226
Held to maturity, 6 to 10 years, amortized cost	3,103
Held to maturity, 6 to 10 years, fair value	3,243
Held to maturity, over 10 years, amortized cost	23,097
Held to maturity, over 10 years, fair value	23,907
Held to maturity, amortized cost	35,881
Held to maturity, fair value	37,015
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	57
Available for sale, under 1 year, fair value	57
Available for sale, 1 to 5 years, amortized cost	217
Available for sale, 1 to 5 years, fair value	216
Available for sale, 6 to 10 years, amortized cost	17
Available for sale, 6 to 10 years, fair value	16
Available for sale, over 10 years, amortized cost	175
Available for sale, over 10 years, fair value	165
Available for sale, amortized cost	466
Available for sale, fair value	454
Held to maturity, under 1 year, amortized cost	105
Held to maturity, under 1 year, fair value	96
Held to maturity, 1 to 5 years, amortized cost	201
Held to maturity, 1 to 5 years, fair value	196
Held to maturity, 6 to 10 years, amortized cost	516
Held to maturity, 6 to 10 years, fair value	494
Held to maturity, over 10 years, amortized cost	3,233
Held to maturity, over 10 years, fair value	3,122
Held to maturity, amortized cost	4,055
Held to maturity, fair value	3,908
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	85
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	85
Asset-backed securities, collateralized loan 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	923
Available for sale, 1 to 5 years, fair value	888
Available for sale, 6 to 10 years, amortized cost	891
Available for sale, 6 to 10 years, fair value	843
Available for sale, over 10 years, amortized cost	117
Available for sale, over 10 years, fair value	110
Available for sale, amortized cost	1,931
Available for sale, fair value	1,841
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	57
Available for sale, under 1 year, fair value	57
Available for sale, 1 to 5 years, amortized cost	1,140
Available for sale, 1 to 5 years, fair value	1,104
Available for sale, 6 to 10 years, amortized cost	998
Available for sale, 6 to 10 years, fair value	944
Available for sale, over 10 years, amortized cost	292
Available for sale, over 10 years, fair value	275
Available for sale, amortized cost	2,487
Available for sale, fair value	2,380
Held to maturity, under 1 year, amortized cost	105
Held to maturity, under 1 year, fair value	96
Held to maturity, 1 to 5 years, amortized cost	201
Held to maturity, 1 to 5 years, fair value	196
Held to maturity, 6 to 10 years, amortized cost	516
Held to maturity, 6 to 10 years, fair value	494
Held to maturity, over 10 years, amortized cost	3,233
Held to maturity, over 10 years, fair value	3,122
Held to maturity, amortized cost	4,055
Held to maturity, fair value	3,908
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	303
Available for sale, under 1 year, fair value	301
Available for sale, 1 to 5 years, amortized cost	548
Available for sale, 1 to 5 years, fair value	541
Available for sale, 6 to 10 years, amortized cost	143
Available for sale, 6 to 10 years, fair value	141
Available for sale, over 10 years, amortized cost	716
Available for sale, over 10 years, fair value	709
Available for sale, amortized cost	1,710
Available for sale, fair value	1,692
Held to maturity, under 1 year, amortized cost	11
Held to maturity, under 1 year, fair value	11
Held to maturity, 1 to 5 years, amortized cost	26
Held to maturity, 1 to 5 years, fair value	26
Held to maturity, 6 to 10 years, amortized cost	4
Held to maturity, 6 to 10 years, fair value	3
Held to maturity, over 10 years, amortized cost	294
Held to maturity, over 10 years, fair value	337
Held to maturity, amortized cost	335
Held to maturity, fair value	377
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	292
Available for sale, under 1 year, fair value	280
Available for sale, 1 to 5 years, amortized cost	913
Available for sale, 1 to 5 years, fair value	897
Available for sale, 6 to 10 years, amortized cost	362
Available for sale, 6 to 10 years, fair value	349
Available for sale, over 10 years, amortized cost	340
Available for sale, over 10 years, fair value	329
Available for sale, amortized cost	1,907
Available for sale, fair value	1,855
Non-U.S. debt securities, government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	4,920
Available for sale, under 1 year, fair value	4,927
Available for sale, 1 to 5 years, amortized cost	7,270
Available for sale, 1 to 5 years, fair value	7,375
Available for sale, 6 to 10 years, amortized cost	402
Available for sale, 6 to 10 years, fair value	406
Available for sale, over 10 years, amortized cost	360
Available for sale, over 10 years, fair value	347
Available for sale, amortized cost	12,952
Available for sale, fair value	13,055
Held to maturity, under 1 year, amortized cost	279
Held to maturity, under 1 year, fair value	280
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	279
Held to maturity, fair value	280
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	699
Available for sale, under 1 year, fair value	699
Available for sale, 1 to 5 years, amortized cost	6,692
Available for sale, 1 to 5 years, fair value	6,712
Available for sale, 6 to 10 years, amortized cost	1,297
Available for sale, 6 to 10 years, fair value	1,290
Available for sale, over 10 years, amortized cost	73
Available for sale, over 10 years, fair value	73
Available for sale, amortized cost	8,761
Available for sale, fair value	8,774
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	6,214
Available for sale, under 1 year, fair value	6,207
Available for sale, 1 to 5 years, amortized cost	15,423
Available for sale, 1 to 5 years, fair value	15,525
Available for sale, 6 to 10 years, amortized cost	2,204
Available for sale, 6 to 10 years, fair value	2,186
Available for sale, over 10 years, amortized cost	1,489
Available for sale, over 10 years, fair value	1,458
Available for sale, amortized cost	25,330
Available for sale, fair value	25,376
Held to maturity, under 1 year, amortized cost	290
Held to maturity, under 1 year, fair value	291
Held to maturity, 1 to 5 years, amortized cost	26
Held to maturity, 1 to 5 years, fair value	26
Held to maturity, 6 to 10 years, amortized cost	4
Held to maturity, 6 to 10 years, fair value	3
Held to maturity, over 10 years, amortized cost	294
Held to maturity, over 10 years, fair value	337
Held to maturity, amortized cost	614
Held to maturity, fair value	657
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	232
Available for sale, under 1 year, fair value	232
Available for sale, 1 to 5 years, amortized cost	648
Available for sale, 1 to 5 years, fair value	648
Available for sale, 6 to 10 years, amortized cost	531
Available for sale, 6 to 10 years, fair value	559
Available for sale, over 10 years, amortized cost	313
Available for sale, over 10 years, fair value	326
Available for sale, amortized cost	1,724
Available for sale, fair value	1,765
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	96
Available for sale, over 10 years, fair value	96
Available for sale, amortized cost	96
Available for sale, fair value	96
Held to maturity, under 1 year, amortized cost	2
Held to maturity, under 1 year, fair value	2
Held to maturity, 1 to 5 years, amortized cost	279
Held to maturity, 1 to 5 years, fair value	283
Held to maturity, 6 to 10 years, amortized cost	13
Held to maturity, 6 to 10 years, fair value	12
Held to maturity, over 10 years, amortized cost	306
Held to maturity, over 10 years, fair value	324
Held to maturity, amortized cost	600
Held to maturity, fair value	621
Total
Contractual Maturities Of Debt Investment Securities [Line Items]
Held to maturity, under 1 year, amortized cost	4,012
Held to maturity, under 1 year, fair value	4,028
Held to maturity, 1 to 5 years, amortized cost	6,572
Held to maturity, 1 to 5 years, fair value	6,731
Held to maturity, 6 to 10 years, amortized cost	3,636
Held to maturity, 6 to 10 years, fair value	3,752
Held to maturity, over 10 years, amortized cost	26,930
Held to maturity, over 10 years, fair value	27,690
Held to maturity, amortized cost	41,150
Held to maturity, fair value	42,201
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	793
Available for sale, under 1 year, fair value	790
Available for sale, 1 to 5 years, amortized cost	1,847
Available for sale, 1 to 5 years, fair value	1,826
Available for sale, 6 to 10 years, amortized cost	97
Available for sale, 6 to 10 years, fair value	96
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	2,737
Available for sale, fair value	2,712
Money Market Liquidity Facility
Contractual Maturities Of Debt Investment Securities [Line Items]
Held to maturity, under 1 year, amortized cost	26,812
Held to maturity, under 1 year, fair value	26,808
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	26,812
Held to maturity, fair value	$ 26,808