Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 9,314	$ 17,740
Available for sale, gross unrealized losses less than 12 months	35	110
Available for sale, fair value 12 months or longer	7,039	6,886
Available for sale, gross unrealized losses 12 months or longer	140	208
Available for sale, fair value total	16,353	24,626
Available for sale, gross unrealized losses total	175	318
Held to maturity, fair value less than 12 months	3,922	9,461
Held-to-maturity, gross unrealized losses, less than 12 months	35	155
Held to maturity, fair value 12 months or longer	25,912	23,757
Held to maturity, gross unrealized losses 12 months or longer	364	583
Held to maturity, fair value total	29,834	33,218
Held to maturity, gross unrealized losses total	399	738
US Treasury and federal agencies, mortgage-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,565	5,058
Available for sale, gross unrealized losses less than 12 months	4	21
Available for sale, fair value 12 months or longer	5,147	5,089
Available for sale, gross unrealized losses 12 months or longer	105	160
Available for sale, fair value total	7,712	10,147
Available for sale, gross unrealized losses total	109	181
Held to maturity, fair value less than 12 months	357	6,502
Held-to-maturity, gross unrealized losses, less than 12 months	1	103
Held to maturity, fair value 12 months or longer	14,205	10,648
Held to maturity, gross unrealized losses 12 months or longer	249	415
Held to maturity, fair value total	14,562	17,150
Held to maturity, gross unrealized losses total	250	518
Total U.S. Treasury and federal agencies
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	2,565	5,058
Available for sale, gross unrealized losses less than 12 months	4	21
Available for sale, fair value 12 months or longer	5,147	5,089
Available for sale, gross unrealized losses 12 months or longer	105	160
Available for sale, fair value total	7,712	10,147
Available for sale, gross unrealized losses total	109	181
Held to maturity, fair value less than 12 months	2,567	8,694
Held-to-maturity, gross unrealized losses, less than 12 months	26	148
Held to maturity, fair value 12 months or longer	25,241	23,051
Held to maturity, gross unrealized losses 12 months or longer	347	569
Held to maturity, fair value total	27,808	31,745
Held to maturity, gross unrealized losses total	373	717
Asset-backed securities, student loans
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	10	106
Available for sale, gross unrealized losses less than 12 months	0	0
Available for sale, fair value 12 months or longer	212	218
Available for sale, gross unrealized losses 12 months or longer	0	1
Available for sale, fair value total	222	324
Available for sale, gross unrealized losses total	0	1
Held to maturity, fair value less than 12 months	1,155	481
Held-to-maturity, gross unrealized losses, less than 12 months	7	4
Held to maturity, fair value 12 months or longer	507	536
Held to maturity, gross unrealized losses 12 months or longer	9	6
Held to maturity, fair value total	1,662	1,017
Held to maturity, gross unrealized losses total	16	10
Asset-backed securities, credit cards
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	89	90
Available for sale, gross unrealized losses less than 12 months	1	0
Available for sale, fair value 12 months or longer	497	493
Available for sale, gross unrealized losses 12 months or longer	25	26
Available for sale, fair value total	586	583
Available for sale, gross unrealized losses total	26	26
Asset-backed securities, collateralized loan obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	586	548
Available for sale, gross unrealized losses less than 12 months	3	2
Available for sale, fair value 12 months or longer	0	0
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	586	548
Available for sale, gross unrealized losses total	3	2
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	685	744
Available for sale, gross unrealized losses less than 12 months	4	2
Available for sale, fair value 12 months or longer	709	711
Available for sale, gross unrealized losses 12 months or longer	25	27
Available for sale, fair value total	1,394	1,455
Available for sale, gross unrealized losses total	29	29
Held to maturity, fair value less than 12 months	1,155	481
Held-to-maturity, gross unrealized losses, less than 12 months	7	4
Held to maturity, fair value 12 months or longer	507	536
Held to maturity, gross unrealized losses 12 months or longer	9	6
Held to maturity, fair value total	1,662	1,017
Held to maturity, gross unrealized losses total	16	10
Non-U.S. debt securities, mortgage-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	890	1,407
Available for sale, gross unrealized losses less than 12 months	3	4
Available for sale, fair value 12 months or longer	111	118
Available for sale, gross unrealized losses 12 months or longer	1	1
Available for sale, fair value total	1,001	1,525
Available for sale, gross unrealized losses total	4	5
Held to maturity, fair value less than 12 months	99	184
Held-to-maturity, gross unrealized losses, less than 12 months	2	2
Held to maturity, fair value 12 months or longer	116	119
Held to maturity, gross unrealized losses 12 months or longer	6	7
Held to maturity, fair value total	215	303
Held to maturity, gross unrealized losses total	8	9
Non-U.S. debt securities, asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	992	1,479
Available for sale, gross unrealized losses less than 12 months	6	6
Available for sale, fair value 12 months or longer	0	0
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	992	1,479
Available for sale, gross unrealized losses total	6	6
Non-U.S. debt securities, government securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	3,345	5,478
Available for sale, gross unrealized losses less than 12 months	14	45
Available for sale, fair value 12 months or longer	0	0
Available for sale, gross unrealized losses 12 months or longer	0	0
Available for sale, fair value total	3,345	5,478
Available for sale, gross unrealized losses total	14	45
Non-U.S. debt securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	721	2,167
Available for sale, gross unrealized losses less than 12 months	2	12
Available for sale, fair value 12 months or longer	189	226
Available for sale, gross unrealized losses 12 months or longer	1	4
Available for sale, fair value total	910	2,393
Available for sale, gross unrealized losses total	3	16
Total non-U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	5,948	10,531
Available for sale, gross unrealized losses less than 12 months	25	67
Available for sale, fair value 12 months or longer	300	344
Available for sale, gross unrealized losses 12 months or longer	2	5
Available for sale, fair value total	6,248	10,875
Available for sale, gross unrealized losses total	27	72
Held to maturity, fair value less than 12 months	99	184
Held-to-maturity, gross unrealized losses, less than 12 months	2	2
Held to maturity, fair value 12 months or longer	116	119
Held to maturity, gross unrealized losses 12 months or longer	6	7
Held to maturity, fair value total	215	303
Held to maturity, gross unrealized losses total	8	9
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	0	365
Available for sale, gross unrealized losses less than 12 months	0	3
Available for sale, fair value 12 months or longer	254	244
Available for sale, gross unrealized losses 12 months or longer	2	4
Available for sale, fair value total	254	609
Available for sale, gross unrealized losses total	2	7
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	0	181
Available for sale, gross unrealized losses less than 12 months	0	3
Available for sale, fair value 12 months or longer	129	14
Available for sale, gross unrealized losses 12 months or longer	1	0
Available for sale, fair value total	129	195
Available for sale, gross unrealized losses total	1	3
Held to maturity, fair value less than 12 months	101	102
Held-to-maturity, gross unrealized losses, less than 12 months	0	1
Held to maturity, fair value 12 months or longer	48	51
Held to maturity, gross unrealized losses 12 months or longer	2	1
Held to maturity, fair value total	149	153
Held to maturity, gross unrealized losses total	2	2
Other U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	116	861
Available for sale, gross unrealized losses less than 12 months	2	14
Available for sale, fair value 12 months or longer	500	484
Available for sale, gross unrealized losses 12 months or longer	5	12
Available for sale, fair value total	616	1,345
Available for sale, gross unrealized losses total	7	26
US Treasury and federal agencies, direct obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Held to maturity, fair value less than 12 months	2,210	2,192
Held-to-maturity, gross unrealized losses, less than 12 months	25	45
Held to maturity, fair value 12 months or longer	11,036	12,403
Held to maturity, gross unrealized losses 12 months or longer	98	154
Held to maturity, fair value total	13,246	14,595
Held to maturity, gross unrealized losses total	$ 123	$ 199

Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position.

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.

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