Investment Securities - Schedule of Gross Pre-Tax Unrealized Losses on Investment Securities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	$ 19,305	$ 18,094
Available for sale, gross unrealized losses less than 12 months	273	131
Available for sale, fair value 12 months or longer	3,757	6,391
Available for sale, gross unrealized losses 12 months or longer	167	137
Available for sale, fair value total	23,062	24,485
Available for sale, gross unrealized losses total	440	268
Held to maturity, fair value less than 12 months	23,812	21,664
Held-to-maturity, gross, less than 12 months	568	150
Held to maturity, fair value 12 months or longer	9,708	9,373
Held to maturity, gross unrealized losses 12 months or longer	396	239
Held to maturity, fair value total	33,520	31,037
Held to maturity, gross unrealized losses total	964	389
US Treasury and federal agencies, direct obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months		0
Available for sale, gross unrealized losses less than 12 months		0
Available for sale, fair value 12 months or longer		67
Available for sale, gross unrealized losses 12 months or longer		1
Available for sale, fair value total		67
Available for sale, gross unrealized losses total		1
Held to maturity, fair value less than 12 months	12,528	14,439
Held-to-maturity, gross, less than 12 months	246	109
Held to maturity, fair value 12 months or longer	3,172	2,447
Held to maturity, gross unrealized losses 12 months or longer	46	34
Held to maturity, fair value total	15,700	16,886
Held to maturity, gross unrealized losses total	292	143
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	7,776	5,161
Available for sale, gross unrealized losses less than 12 months	136	31
Available for sale, fair value 12 months or longer	3,030	3,341
Available for sale, gross unrealized losses 12 months or longer	151	98
Available for sale, fair value total	10,806	8,502
Available for sale, gross unrealized losses total	287	129
Held to maturity, fair value less than 12 months	11,090	6,785
Held-to-maturity, gross, less than 12 months	320	38
Held to maturity, fair value 12 months or longer	5,606	5,988
Held to maturity, gross unrealized losses 12 months or longer	332	187
Held to maturity, fair value total	16,696	12,773
Held to maturity, gross unrealized losses total	652	225
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	7,776	5,161
Available for sale, gross unrealized losses less than 12 months	136	31
Available for sale, fair value 12 months or longer	3,030	3,408
Available for sale, gross unrealized losses 12 months or longer	151	99
Available for sale, fair value total	10,806	8,569
Available for sale, gross unrealized losses total	287	130
Held to maturity, fair value less than 12 months	23,618	21,224
Held-to-maturity, gross, less than 12 months	566	147
Held to maturity, fair value 12 months or longer	8,778	8,435
Held to maturity, gross unrealized losses 12 months or longer	378	221
Held to maturity, fair value total	32,396	29,659
Held to maturity, gross unrealized losses total	944	368
Asset-backed securities, student loans
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	309	0
Available for sale, gross unrealized losses less than 12 months	1	0
Available for sale, fair value 12 months or longer	192	769
Available for sale, gross unrealized losses 12 months or longer	0	4
Available for sale, fair value total	501	769
Available for sale, gross unrealized losses total	1	4
Held to maturity, fair value less than 12 months	99	440
Held-to-maturity, gross, less than 12 months	1	3
Held to maturity, fair value 12 months or longer	559	423
Held to maturity, gross unrealized losses 12 months or longer	7	6
Held to maturity, fair value total	658	863
Held to maturity, gross unrealized losses total	8	9
Asset-backed securities, credit cards
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	491	1,289
Available for sale, gross unrealized losses less than 12 months	23	25
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	491	1,289
Available for sale, gross unrealized losses total	23	25
Asset-backed securities, other
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	326
Available for sale, gross unrealized losses less than 12 months	1
Available for sale, fair value 12 months or longer	0
Available for sale, gross unrealized losses 12 months or longer	0
Available for sale, fair value total	326
Available for sale, gross unrealized losses total	1
Asset-backed securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,126	1,289
Available for sale, gross unrealized losses less than 12 months	25	25
Available for sale, fair value 12 months or longer	192	769
Available for sale, gross unrealized losses 12 months or longer	0	4
Available for sale, fair value total	1,318	2,058
Available for sale, gross unrealized losses total	25	29
Held to maturity, fair value less than 12 months	99	440
Held-to-maturity, gross, less than 12 months	1	3
Held to maturity, fair value 12 months or longer	559	423
Held to maturity, gross unrealized losses 12 months or longer	7	6
Held to maturity, fair value total	658	863
Held to maturity, gross unrealized losses total	8	9
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	756	1,059
Available for sale, gross unrealized losses less than 12 months	2	4
Available for sale, fair value 12 months or longer	63	469
Available for sale, gross unrealized losses 12 months or longer	0	1
Available for sale, fair value total	819	1,528
Available for sale, gross unrealized losses total	2	5
Held to maturity, fair value less than 12 months	93	0
Held-to-maturity, gross, less than 12 months	1	0
Held to maturity, fair value 12 months or longer	133	239
Held to maturity, gross unrealized losses 12 months or longer	4	6
Held to maturity, fair value total	226	239
Held to maturity, gross unrealized losses total	5	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	6,216	7,629
Available for sale, gross unrealized losses less than 12 months	48	48
Available for sale, fair value 12 months or longer	0	68
Available for sale, gross unrealized losses 12 months or longer	0	1
Available for sale, fair value total	6,216	7,697
Available for sale, gross unrealized losses total	48	49
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	1,254	816
Available for sale, gross unrealized losses less than 12 months	15	4
Available for sale, fair value 12 months or longer	56	289
Available for sale, gross unrealized losses 12 months or longer	1	2
Available for sale, fair value total	1,310	1,105
Available for sale, gross unrealized losses total	16	6
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	8,226	9,504
Available for sale, gross unrealized losses less than 12 months	65	56
Available for sale, fair value 12 months or longer	119	826
Available for sale, gross unrealized losses 12 months or longer	1	4
Available for sale, fair value total	8,345	10,330
Available for sale, gross unrealized losses total	66	60
Held to maturity, fair value less than 12 months	93	0
Held-to-maturity, gross, less than 12 months	1	0
Held to maturity, fair value 12 months or longer	133	239
Held to maturity, gross unrealized losses 12 months or longer	4	6
Held to maturity, fair value total	226	239
Held to maturity, gross unrealized losses total	5	6
State and political subdivisions
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	563	734
Available for sale, gross unrealized losses less than 12 months	7	6
Available for sale, fair value 12 months or longer	233	901
Available for sale, gross unrealized losses 12 months or longer	6	17
Available for sale, fair value total	796	1,635
Available for sale, gross unrealized losses total	13	23
Collateralized mortgage obligations
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	232	399
Available for sale, gross unrealized losses less than 12 months	4	5
Available for sale, fair value 12 months or longer	70	136
Available for sale, gross unrealized losses 12 months or longer	2	4
Available for sale, fair value total	302	535
Available for sale, gross unrealized losses total	6	9
Held to maturity, fair value less than 12 months	2	0
Held-to-maturity, gross, less than 12 months	0	0
Held to maturity, fair value 12 months or longer	238	276
Held to maturity, gross unrealized losses 12 months or longer	7	6
Held to maturity, fair value total	240	276
Held to maturity, gross unrealized losses total	7	6
Other U.S. debt securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months	1,382	1,007
Available for sale, gross unrealized losses less than 12 months	36	8
Available for sale, fair value 12 months or longer	113	345
Available for sale, gross unrealized losses 12 months or longer	7	7
Available for sale, fair value total	1,495	1,352
Available for sale, gross unrealized losses total	$ 43	15
U.S. equity securities
Gross Pre-Tax Unrealized Losses On Investment Securities [Line Items]
Available for sale, fair value less than 12 months		0
Available for sale, gross unrealized losses less than 12 months		0
Available for sale, fair value 12 months or longer		6
Available for sale, gross unrealized losses 12 months or longer		2
Available for sale, fair value total		6
Available for sale, gross unrealized losses total		$ 2

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

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