Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	$ 7,825
Available for sale, 1 to 5 Years	18,911
Available for sale, 6 to 10 Years	8,109
Available for sale, over 10 Years	19,912
Available-for-sale, fair value	54,757	$ 45,148
Held to maturity, under 1 Year	4,681
Held to maturity, 1 to 5 Years	8,353
Held to maturity, 6 to 10 Years	2,339
Held to maturity, over 10 Years	23,746
Held to maturity, amortized cost	39,119	41,914
US Treasury and federal agencies, direct obligations
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	236
Available for sale, 1 to 5 Years	809
Available for sale, 6 to 10 Years	994
Available for sale, over 10 Years	0
Available-for-sale, fair value	2,039	1,039
Held to maturity, under 1 Year	4,316
Held to maturity, 1 to 5 Years	7,427
Held to maturity, 6 to 10 Years	7
Held to maturity, over 10 Years	31
Held to maturity, amortized cost	11,781	14,794
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	122
Available for sale, 1 to 5 Years	974
Available for sale, 6 to 10 Years	3,085
Available for sale, over 10 Years	18,198
Available-for-sale, fair value	22,379	15,968
Held to maturity, under 1 Year	38
Held to maturity, 1 to 5 Years	214
Held to maturity, 6 to 10 Years	1,991
Held to maturity, over 10 Years	19,723
Held to maturity, amortized cost	21,966	21,647
Total U.S. Treasury and federal agencies
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	358
Available for sale, 1 to 5 Years	1,783
Available for sale, 6 to 10 Years	4,079
Available for sale, over 10 Years	18,198
Available-for-sale, fair value	24,418	17,007
Held to maturity, under 1 Year	4,354
Held to maturity, 1 to 5 Years	7,641
Held to maturity, 6 to 10 Years	1,998
Held to maturity, over 10 Years	19,754
Held to maturity, amortized cost	33,747	36,441
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	28
Available for sale, 1 to 5 Years	265
Available for sale, 6 to 10 Years	119
Available for sale, over 10 Years	59
Available-for-sale, fair value	471	541
Held to maturity, under 1 Year	47
Held to maturity, 1 to 5 Years	265
Held to maturity, 6 to 10 Years	324
Held to maturity, over 10 Years	3,245
Held to maturity, amortized cost	3,881	3,191
Asset-backed securities, credit cards
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	90
Available for sale, over 10 Years	0
Available-for-sale, fair value	90	583
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	30
Available for sale, 1 to 5 Years	548
Available for sale, 6 to 10 Years	751
Available for sale, over 10 Years	117
Available-for-sale, fair value	1,446	593
Held to maturity, amortized cost	0	1
Total asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	58
Available for sale, 1 to 5 Years	813
Available for sale, 6 to 10 Years	960
Available for sale, over 10 Years	176
Available-for-sale, fair value	2,007	1,717
Held to maturity, under 1 Year	47
Held to maturity, 1 to 5 Years	265
Held to maturity, 6 to 10 Years	324
Held to maturity, over 10 Years	3,245
Held to maturity, amortized cost	3,881	3,385
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	336
Available for sale, 1 to 5 Years	569
Available for sale, 6 to 10 Years	202
Available for sale, over 10 Years	810
Available-for-sale, fair value	1,917	1,682
Held to maturity, under 1 Year	96
Held to maturity, 1 to 5 Years	34
Held to maturity, 6 to 10 Years	4
Held to maturity, over 10 Years	337
Held to maturity, amortized cost	471	638
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	473
Available for sale, 1 to 5 Years	718
Available for sale, 6 to 10 Years	445
Available for sale, over 10 Years	195
Available-for-sale, fair value	1,831	1,574
Held to maturity, amortized cost	0	223
Non-U.S. debt securities, government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	5,231
Available for sale, 1 to 5 Years	6,609
Available for sale, 6 to 10 Years	1,349
Available for sale, over 10 Years	0
Available-for-sale, fair value	13,189	12,793
Held to maturity, under 1 Year	184
Held to maturity, 1 to 5 Years	110
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	294	358
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	647
Available for sale, 1 to 5 Years	5,889
Available for sale, 6 to 10 Years	441
Available for sale, over 10 Years	21
Available-for-sale, fair value	6,998	6,602
Held to maturity, amortized cost	0	46
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	6,687
Available for sale, 1 to 5 Years	13,785
Available for sale, 6 to 10 Years	2,437
Available for sale, over 10 Years	1,026
Available-for-sale, fair value	23,935	22,651
Held to maturity, under 1 Year	280
Held to maturity, 1 to 5 Years	144
Held to maturity, 6 to 10 Years	4
Held to maturity, over 10 Years	337
Held to maturity, amortized cost	765	1,265
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	146
Available for sale, 1 to 5 Years	784
Available for sale, 6 to 10 Years	490
Available for sale, over 10 Years	399
Available-for-sale, fair value	1,819	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	113
Available-for-sale, fair value	113	197
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	303
Held to maturity, 6 to 10 Years	13
Held to maturity, over 10 Years	410
Held to maturity, amortized cost	726	823
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	576
Available for sale, 1 to 5 Years	1,746
Available for sale, 6 to 10 Years	143
Available for sale, over 10 Years	0
Available-for-sale, fair value	$ 2,465	$ 1,658

Contractual Maturities Of Debt Investment Securities [Line Items]

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