Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	$ 5,858
Available for sale, 1 to 5 Years	17,530
Available for sale, 6 to 10 Years	7,727
Available for sale, over 10 Years	17,887
Available-for-sale, fair value	49,002	$ 45,148
Held to maturity, under 1 Year	3,826
Held to maturity, 1 to 5 Years	11,053
Held to maturity, 6 to 10 Years	1,953
Held to maturity, over 10 Years	24,313
Held to maturity, amortized cost	41,145	41,914
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	235
Available for sale, 1 to 5 Years	806
Available for sale, 6 to 10 Years	0
Available for sale, over 10 Years	0
Available-for-sale, fair value	1,041	1,039
Held to maturity, under 1 Year	3,225
Held to maturity, 1 to 5 Years	10,096
Held to maturity, 6 to 10 Years	11
Held to maturity, over 10 Years	37
Held to maturity, amortized cost	13,369	14,794
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	44
Available for sale, 1 to 5 Years	991
Available for sale, 6 to 10 Years	2,490
Available for sale, over 10 Years	16,518
Available-for-sale, fair value	20,043	15,968
Held to maturity, under 1 Year	31
Held to maturity, 1 to 5 Years	236
Held to maturity, 6 to 10 Years	1,538
Held to maturity, over 10 Years	20,763
Held to maturity, amortized cost	22,568	21,647
Total U.S. Treasury and federal agencies
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	279
Available for sale, 1 to 5 Years	1,797
Available for sale, 6 to 10 Years	2,490
Available for sale, over 10 Years	16,518
Available-for-sale, fair value	21,084	17,007
Held to maturity, under 1 Year	3,256
Held to maturity, 1 to 5 Years	10,332
Held to maturity, 6 to 10 Years	1,549
Held to maturity, over 10 Years	20,800
Held to maturity, amortized cost	35,937	36,441
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	94
Available for sale, 1 to 5 Years	160
Available for sale, 6 to 10 Years	161
Available for sale, over 10 Years	66
Available-for-sale, fair value	481	541
Held to maturity, under 1 Year	7
Held to maturity, 1 to 5 Years	255
Held to maturity, 6 to 10 Years	383
Held to maturity, over 10 Years	2,641
Held to maturity, amortized cost	3,286	3,191
Asset-backed securities, credit cards
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	200
Available for sale, 1 to 5 Years	297
Available for sale, 6 to 10 Years	89
Available for sale, over 10 Years	0
Available-for-sale, fair value	586	583
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	0
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	0	193
Asset-backed securities, collateralized loan obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	0
Available for sale, 1 to 5 Years	418
Available for sale, 6 to 10 Years	423
Available for sale, over 10 Years	45
Available-for-sale, fair value	886	593
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	0
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	1
Held to maturity, amortized cost	1	1
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	294
Available for sale, 1 to 5 Years	875
Available for sale, 6 to 10 Years	673
Available for sale, over 10 Years	111
Available-for-sale, fair value	1,953	1,717
Held to maturity, under 1 Year	7
Held to maturity, 1 to 5 Years	255
Held to maturity, 6 to 10 Years	383
Held to maturity, over 10 Years	2,642
Held to maturity, amortized cost	3,287	3,385
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	266
Available for sale, 1 to 5 Years	552
Available for sale, 6 to 10 Years	171
Available for sale, over 10 Years	528
Available-for-sale, fair value	1,517	1,682
Held to maturity, under 1 Year	134
Held to maturity, 1 to 5 Years	40
Held to maturity, 6 to 10 Years	7
Held to maturity, over 10 Years	394
Held to maturity, amortized cost	575	638
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	368
Available for sale, 1 to 5 Years	561
Available for sale, 6 to 10 Years	446
Available for sale, over 10 Years	136
Available-for-sale, fair value	1,511	1,574
Held to maturity, under 1 Year	98
Held to maturity, 1 to 5 Years	0
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	98	223
Non-U.S. debt securities, government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	3,178
Available for sale, 1 to 5 Years	6,802
Available for sale, 6 to 10 Years	2,592
Available for sale, over 10 Years	0
Available-for-sale, fair value	12,572	12,793
Held to maturity, under 1 Year	286
Held to maturity, 1 to 5 Years	113
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	399	358
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	1,141
Available for sale, 1 to 5 Years	4,860
Available for sale, 6 to 10 Years	554
Available for sale, over 10 Years	21
Available-for-sale, fair value	6,576	6,602
Held to maturity, under 1 Year	44
Held to maturity, 1 to 5 Years	0
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	44	46
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	4,953
Available for sale, 1 to 5 Years	12,775
Available for sale, 6 to 10 Years	3,763
Available for sale, over 10 Years	685
Available-for-sale, fair value	22,176	22,651
Held to maturity, under 1 Year	562
Held to maturity, 1 to 5 Years	153
Held to maturity, 6 to 10 Years	7
Held to maturity, over 10 Years	394
Held to maturity, amortized cost	1,116	1,265
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	180
Available for sale, 1 to 5 Years	791
Available for sale, 6 to 10 Years	525
Available for sale, over 10 Years	444
Available-for-sale, fair value	1,940	1,918
Collateralized mortgage obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	0
Available for sale, 1 to 5 Years	0
Available for sale, 6 to 10 Years	0
Available for sale, over 10 Years	129
Available-for-sale, fair value	129	197
Held to maturity, under 1 Year	1
Held to maturity, 1 to 5 Years	313
Held to maturity, 6 to 10 Years	14
Held to maturity, over 10 Years	477
Held to maturity, amortized cost	805	823
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	152
Available for sale, 1 to 5 Years	1,292
Available for sale, 6 to 10 Years	276
Available for sale, over 10 Years	0
Available-for-sale, fair value	$ 1,720	$ 1,658