Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) $ in Millions	Dec. 31, 2019 USD ($)
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	$ 8,216
Available for sale, under 1 year, fair value	8,230
Available for sale, 1 to 5 years, amortized cost	21,041
Available for sale, 1 to 5 years, fair value	21,247
Available for sale, 6 to 10 years, amortized cost	8,609
Available for sale, 6 to 10 years, fair value	8,631
Available for sale, over 10 years, amortized cost	15,448
Available for sale, over 10 years, fair value	15,707
Available for sale, amortized cost	53,314
Available for sale, fair value	53,815
Held to maturity, under 1 year, amortized cost	4,567
Held to maturity, under 1 year, fair value	4,562
Held to maturity, 1 to 5 years, amortized cost	7,122
Held to maturity, 1 to 5 years, fair value	7,150
Held to maturity, 6 to 10 years, amortized cost	2,945
Held to maturity, 6 to 10 years, fair value	2,963
Held to maturity, over 10 years, amortized cost	27,148
Held to maturity, over 10 years, fair value	27,482
Held to maturity, amortized cost	41,782
Held to maturity, fair value	42,157
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	1,050
Available for sale, under 1 year, fair value	1,058
Available for sale, 1 to 5 years, amortized cost	1,009
Available for sale, 1 to 5 years, fair value	1,010
Available for sale, 6 to 10 years, amortized cost	1,448
Available for sale, 6 to 10 years, fair value	1,419
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	3,507
Available for sale, fair value	3,487
Held to maturity, under 1 year, amortized cost	4,116
Held to maturity, under 1 year, fair value	4,114
Held to maturity, 1 to 5 years, amortized cost	6,161
Held to maturity, 1 to 5 years, fair value	6,185
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	29
Held to maturity, over 10 years, fair value	29
Held to maturity, amortized cost	10,311
Held to maturity, fair value	10,333
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	116
Available for sale, under 1 year, fair value	118
Available for sale, 1 to 5 years, amortized cost	971
Available for sale, 1 to 5 years, fair value	970
Available for sale, 6 to 10 years, amortized cost	2,954
Available for sale, 6 to 10 years, fair value	2,951
Available for sale, over 10 years, amortized cost	13,558
Available for sale, over 10 years, fair value	13,799
Available for sale, amortized cost	17,599
Available for sale, fair value	17,838
Held to maturity, under 1 year, amortized cost	9
Held to maturity, under 1 year, fair value	9
Held to maturity, 1 to 5 years, amortized cost	438
Held to maturity, 1 to 5 years, fair value	439
Held to maturity, 6 to 10 years, amortized cost	2,515
Held to maturity, 6 to 10 years, fair value	2,539
Held to maturity, over 10 years, amortized cost	23,335
Held to maturity, over 10 years, fair value	23,581
Held to maturity, amortized cost	26,297
Held to maturity, fair value	26,568
Total U.S. Treasury and federal agencies
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	1,166
Available for sale, under 1 year, fair value	1,176
Available for sale, 1 to 5 years, amortized cost	1,980
Available for sale, 1 to 5 years, fair value	1,980
Available for sale, 6 to 10 years, amortized cost	4,402
Available for sale, 6 to 10 years, fair value	4,370
Available for sale, over 10 years, amortized cost	13,558
Available for sale, over 10 years, fair value	13,799
Available for sale, amortized cost	21,106
Available for sale, fair value	21,325
Held to maturity, under 1 year, amortized cost	4,125
Held to maturity, under 1 year, fair value	4,123
Held to maturity, 1 to 5 years, amortized cost	6,599
Held to maturity, 1 to 5 years, fair value	6,624
Held to maturity, 6 to 10 years, amortized cost	2,520
Held to maturity, 6 to 10 years, fair value	2,544
Held to maturity, over 10 years, amortized cost	23,364
Held to maturity, over 10 years, fair value	23,610
Held to maturity, amortized cost	36,608
Held to maturity, fair value	36,901
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	72
Available for sale, under 1 year, fair value	72
Available for sale, 1 to 5 years, amortized cost	185
Available for sale, 1 to 5 years, fair value	184
Available for sale, 6 to 10 years, amortized cost	96
Available for sale, 6 to 10 years, fair value	96
Available for sale, over 10 years, amortized cost	180
Available for sale, over 10 years, fair value	179
Available for sale, amortized cost	533
Available for sale, fair value	531
Held to maturity, under 1 year, amortized cost	96
Held to maturity, under 1 year, fair value	92
Held to maturity, 1 to 5 years, amortized cost	207
Held to maturity, 1 to 5 years, fair value	206
Held to maturity, 6 to 10 years, amortized cost	408
Held to maturity, 6 to 10 years, fair value	402
Held to maturity, over 10 years, amortized cost	3,072
Held to maturity, over 10 years, fair value	3,051
Held to maturity, amortized cost	3,783
Held to maturity, fair value	3,751
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	89
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	89
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	745
Available for sale, 1 to 5 years, fair value	745
Available for sale, 6 to 10 years, amortized cost	959
Available for sale, 6 to 10 years, fair value	958
Available for sale, over 10 years, amortized cost	117
Available for sale, over 10 years, fair value	117
Available for sale, amortized cost	1,821
Available for sale, fair value	1,820
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	72
Available for sale, under 1 year, fair value	72
Available for sale, 1 to 5 years, amortized cost	930
Available for sale, 1 to 5 years, fair value	929
Available for sale, 6 to 10 years, amortized cost	1,145
Available for sale, 6 to 10 years, fair value	1,143
Available for sale, over 10 years, amortized cost	297
Available for sale, over 10 years, fair value	296
Available for sale, amortized cost	2,444
Available for sale, fair value	2,440
Held to maturity, under 1 year, amortized cost	96
Held to maturity, under 1 year, fair value	92
Held to maturity, 1 to 5 years, amortized cost	207
Held to maturity, 1 to 5 years, fair value	206
Held to maturity, 6 to 10 years, amortized cost	408
Held to maturity, 6 to 10 years, fair value	402
Held to maturity, over 10 years, amortized cost	3,072
Held to maturity, over 10 years, fair value	3,051
Held to maturity, amortized cost	3,783
Held to maturity, fair value	3,751
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	430
Available for sale, under 1 year, fair value	430
Available for sale, 1 to 5 years, amortized cost	568
Available for sale, 1 to 5 years, fair value	569
Available for sale, 6 to 10 years, amortized cost	196
Available for sale, 6 to 10 years, fair value	196
Available for sale, over 10 years, amortized cost	784
Available for sale, over 10 years, fair value	785
Available for sale, amortized cost	1,978
Available for sale, fair value	1,980
Held to maturity, under 1 year, amortized cost	16
Held to maturity, under 1 year, fair value	16
Held to maturity, 1 to 5 years, amortized cost	33
Held to maturity, 1 to 5 years, fair value	33
Held to maturity, 6 to 10 years, amortized cost	4
Held to maturity, 6 to 10 years, fair value	4
Held to maturity, over 10 years, amortized cost	313
Held to maturity, over 10 years, fair value	390
Held to maturity, amortized cost	366
Held to maturity, fair value	443
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	487
Available for sale, under 1 year, fair value	487
Available for sale, 1 to 5 years, amortized cost	981
Available for sale, 1 to 5 years, fair value	981
Available for sale, 6 to 10 years, amortized cost	366
Available for sale, 6 to 10 years, fair value	366
Available for sale, over 10 years, amortized cost	345
Available for sale, over 10 years, fair value	345
Available for sale, amortized cost	2,179
Available for sale, fair value	2,179
Non-U.S. debt securities, government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	4,183
Available for sale, under 1 year, fair value	4,183
Available for sale, 1 to 5 years, amortized cost	7,270
Available for sale, 1 to 5 years, fair value	7,381
Available for sale, 6 to 10 years, amortized cost	791
Available for sale, 6 to 10 years, fair value	809
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	12,244
Available for sale, fair value	12,373
Held to maturity, under 1 year, amortized cost	328
Held to maturity, under 1 year, fair value	328
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	328
Held to maturity, fair value	328
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	883
Available for sale, under 1 year, fair value	884
Available for sale, 1 to 5 years, amortized cost	6,634
Available for sale, 1 to 5 years, fair value	6,689
Available for sale, 6 to 10 years, amortized cost	1,057
Available for sale, 6 to 10 years, fair value	1,063
Available for sale, over 10 years, amortized cost	19
Available for sale, over 10 years, fair value	22
Available for sale, amortized cost	8,593
Available for sale, fair value	8,658
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	5,983
Available for sale, under 1 year, fair value	5,984
Available for sale, 1 to 5 years, amortized cost	15,453
Available for sale, 1 to 5 years, fair value	15,620
Available for sale, 6 to 10 years, amortized cost	2,410
Available for sale, 6 to 10 years, fair value	2,434
Available for sale, over 10 years, amortized cost	1,148
Available for sale, over 10 years, fair value	1,152
Available for sale, amortized cost	24,994
Available for sale, fair value	25,190
Held to maturity, under 1 year, amortized cost	344
Held to maturity, under 1 year, fair value	344
Held to maturity, 1 to 5 years, amortized cost	33
Held to maturity, 1 to 5 years, fair value	33
Held to maturity, 6 to 10 years, amortized cost	4
Held to maturity, 6 to 10 years, fair value	4
Held to maturity, over 10 years, amortized cost	313
Held to maturity, over 10 years, fair value	390
Held to maturity, amortized cost	694
Held to maturity, fair value	771
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	236
Available for sale, under 1 year, fair value	238
Available for sale, 1 to 5 years, amortized cost	622
Available for sale, 1 to 5 years, fair value	635
Available for sale, 6 to 10 years, amortized cost	526
Available for sale, 6 to 10 years, fair value	554
Available for sale, over 10 years, amortized cost	341
Available for sale, over 10 years, fair value	356
Available for sale, amortized cost	1,725
Available for sale, fair value	1,783
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	104
Available for sale, over 10 years, fair value	104
Available for sale, amortized cost	104
Available for sale, fair value	104
Held to maturity, under 1 year, amortized cost	2
Held to maturity, under 1 year, fair value	3
Held to maturity, 1 to 5 years, amortized cost	283
Held to maturity, 1 to 5 years, fair value	287
Held to maturity, 6 to 10 years, amortized cost	13
Held to maturity, 6 to 10 years, fair value	13
Held to maturity, over 10 years, amortized cost	399
Held to maturity, over 10 years, fair value	431
Held to maturity, amortized cost	697
Held to maturity, fair value	734
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 year, amortized cost	759
Available for sale, under 1 year, fair value	760
Available for sale, 1 to 5 years, amortized cost	2,056
Available for sale, 1 to 5 years, fair value	2,083
Available for sale, 6 to 10 years, amortized cost	126
Available for sale, 6 to 10 years, fair value	130
Available for sale, over 10 years, amortized cost	0
Available for sale, over 10 years, fair value	0
Available for sale, amortized cost	2,941
Available for sale, fair value	$ 2,973