Investment Securities - Schedule of Contractual Maturities of Debt Securities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	$ 7,268
Available for sale, 1 to 5 Years	19,722
Available for sale, 6 to 10 Years	7,188
Available for sale, over 10 Years	19,064
Available-for-sale, fair value	53,242	$ 45,148
Held to maturity, under 1 Year	4,719
Held to maturity, 1 to 5 Years	9,123
Held to maturity, 6 to 10 Years	2,151
Held to maturity, over 10 Years	23,243
Held to maturity, amortized cost	39,236	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	810
Available for sale, 6 to 10 Years	0
Available for sale, over 10 Years	0
Available-for-sale, fair value	1,045	1,039
Held to maturity, under 1 Year	4,198
Held to maturity, 1 to 5 Years	8,193
Held to maturity, 6 to 10 Years	7
Held to maturity, over 10 Years	35
Held to maturity, amortized cost	12,433	14,794
US Treasury and federal agencies, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	70
Available for sale, 1 to 5 Years	984
Available for sale, 6 to 10 Years	2,798
Available for sale, over 10 Years	17,381
Available-for-sale, fair value	21,233	15,968
Held to maturity, under 1 Year	30
Held to maturity, 1 to 5 Years	225
Held to maturity, 6 to 10 Years	1,760
Held to maturity, over 10 Years	19,451
Held to maturity, amortized cost	21,466	21,647
Total U.S. Treasury and federal agencies
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	305
Available for sale, 1 to 5 Years	1,794
Available for sale, 6 to 10 Years	2,798
Available for sale, over 10 Years	17,381
Available-for-sale, fair value	22,278	17,007
Held to maturity, under 1 Year	4,228
Held to maturity, 1 to 5 Years	8,418
Held to maturity, 6 to 10 Years	1,767
Held to maturity, over 10 Years	19,486
Held to maturity, amortized cost	33,899	36,441
Asset-backed securities, student loans
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	80
Available for sale, 1 to 5 Years	312
Available for sale, 6 to 10 Years	144
Available for sale, over 10 Years	62
Available-for-sale, fair value	598	541
Held to maturity, under 1 Year	44
Held to maturity, 1 to 5 Years	245
Held to maturity, 6 to 10 Years	367
Held to maturity, over 10 Years	2,947
Held to maturity, amortized cost	3,603	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	151
Available for sale, 6 to 10 Years	89
Available for sale, over 10 Years	0
Available-for-sale, fair value	240	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	30
Available for sale, 1 to 5 Years	534
Available for sale, 6 to 10 Years	793
Available for sale, over 10 Years	95
Available-for-sale, fair value	1,452	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	0
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	110
Available for sale, 1 to 5 Years	997
Available for sale, 6 to 10 Years	1,026
Available for sale, over 10 Years	157
Available-for-sale, fair value	2,290	1,717
Held to maturity, under 1 Year	44
Held to maturity, 1 to 5 Years	245
Held to maturity, 6 to 10 Years	367
Held to maturity, over 10 Years	2,947
Held to maturity, amortized cost	3,603	3,385
Non-U.S. debt securities, mortgage-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	273
Available for sale, 1 to 5 Years	640
Available for sale, 6 to 10 Years	225
Available for sale, over 10 Years	732
Available-for-sale, fair value	1,870	1,682
Held to maturity, under 1 Year	103
Held to maturity, 1 to 5 Years	38
Held to maturity, 6 to 10 Years	4
Held to maturity, over 10 Years	356
Held to maturity, amortized cost	501	638
Non-U.S. debt securities, asset-backed securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	441
Available for sale, 1 to 5 Years	548
Available for sale, 6 to 10 Years	451
Available for sale, over 10 Years	215
Available-for-sale, fair value	1,655	1,574
Held to maturity, under 1 Year	95
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	95	223
Non-U.S. debt securities, government securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	4,611
Available for sale, 1 to 5 Years	7,803
Available for sale, 6 to 10 Years	1,404
Available for sale, over 10 Years	0
Available-for-sale, fair value	13,818	12,793
Held to maturity, under 1 Year	248
Held to maturity, 1 to 5 Years	114
Held to maturity, 6 to 10 Years	0
Held to maturity, over 10 Years	0
Held to maturity, amortized cost	362	358
Non-U.S. debt securities, other
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	918
Available for sale, 1 to 5 Years	5,652
Available for sale, 6 to 10 Years	513
Available for sale, over 10 Years	21
Available-for-sale, fair value	7,104	6,602
Held to maturity, under 1 Year	1
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	1	46
Total non-U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	6,243
Available for sale, 1 to 5 Years	14,643
Available for sale, 6 to 10 Years	2,593
Available for sale, over 10 Years	968
Available-for-sale, fair value	24,447	22,651
Held to maturity, under 1 Year	447
Held to maturity, 1 to 5 Years	152
Held to maturity, 6 to 10 Years	4
Held to maturity, over 10 Years	356
Held to maturity, amortized cost	959	1,265
State and political subdivisions
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	201
Available for sale, 1 to 5 Years	720
Available for sale, 6 to 10 Years	545
Available for sale, over 10 Years	436
Available-for-sale, fair value	1,902	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	122
Available-for-sale, fair value	122	197
Held to maturity, under 1 Year	0
Held to maturity, 1 to 5 Years	308
Held to maturity, 6 to 10 Years	13
Held to maturity, over 10 Years	454
Held to maturity, amortized cost	775	823
Other U.S. debt securities
Contractual Maturities Of Debt Investment Securities [Line Items]
Available for sale, under 1 Year	409
Available for sale, 1 to 5 Years	1,568
Available for sale, 6 to 10 Years	226
Available for sale, over 10 Years	0
Available-for-sale, fair value	$ 2,203	$ 1,658

Contractual Maturities Of Debt Investment Securities [Line Items]

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