Investment Securities - Fair Value and Gross Unrealized Losses by Aging Category (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Available-for-sale securities
Less than 12 months, Fair value	$ 36,181	$ 50,325
Less than 12 months, Gross unrealized losses	245	550
12 months or more, Fair Value	29,230	36,706
12 months or more, Gross unrealized losses	367	993
Total fair value	65,411	87,031
Total gross unrealized losses	612	1,543
Held-to-maturity securities
Less than 12 months, Fair value	18	4,397
Less than 12 months, Gross unrealized losses	0	23
12 months or more, Fair value	5,666	8,196
12 months or more, Gross unrealized losses	78	192
Total fair value	5,684	12,593
Total gross unrealized losses	78	215
Total investment securities with gross unrealized losses
Less than 12 months, Fair value	36,199	54,722
Less than 12 months, Gross unrealized losses	245	573
12 months or more, Fair value	34,896	44,902
12 months or more, Gross unrealized losses	445	1,185
Total fair value	71,095	99,624
Total gross unrealized losses	690	1,758
Total mortgage-backed securities
Available-for-sale securities
Less than 12 months, Fair value	8,843	20,160
Less than 12 months, Gross unrealized losses	127	333
12 months or more, Fair Value	21,525	27,510
12 months or more, Gross unrealized losses	307	825
Total fair value	30,368	47,670
Total gross unrealized losses	434	1,158
Held-to-maturity securities
Less than 12 months, Fair value	18	4,385
Less than 12 months, Gross unrealized losses	0	23
12 months or more, Fair value	5,315	7,082
12 months or more, Gross unrealized losses	77	177
Total fair value	5,333	11,467
Total gross unrealized losses	77	200
U.S. government agencies
Available-for-sale securities
Less than 12 months, Fair value	8,230	17,656
Less than 12 months, Gross unrealized losses	124	318
12 months or more, Fair Value	17,215	22,728
12 months or more, Gross unrealized losses	228	656
Total fair value	25,445	40,384
Total gross unrealized losses	352	974
Held-to-maturity securities
Less than 12 months, Fair value	18	4,385
Less than 12 months, Gross unrealized losses	0	23
12 months or more, Fair value	5,315	7,082
12 months or more, Gross unrealized losses	77	177
Total fair value	5,333	11,467
Total gross unrealized losses	77	200
Residential: U.S.
Available-for-sale securities
Less than 12 months, Fair value	12	623
Less than 12 months, Gross unrealized losses	0	4
12 months or more, Fair Value	1,404	1,445
12 months or more, Gross unrealized losses	18	27
Total fair value	1,416	2,068
Total gross unrealized losses	18	31
Residential: Non-U.S.
Available-for-sale securities
Less than 12 months, Fair value	218	907
Less than 12 months, Gross unrealized losses	1	5
12 months or more, Fair Value	499	165
12 months or more, Gross unrealized losses	2	1
Total fair value	717	1,072
Total gross unrealized losses	3	6
Commercial
Available-for-sale securities
Less than 12 months, Fair value	383	974
Less than 12 months, Gross unrealized losses	2	6
12 months or more, Fair Value	2,407	3,172
12 months or more, Gross unrealized losses	59	141
Total fair value	2,790	4,146
Total gross unrealized losses	61	147
U.S. Treasury and government agencies
Available-for-sale securities
Less than 12 months, Fair value	8,112	4,792
Less than 12 months, Gross unrealized losses	29	7
12 months or more, Fair Value	218	2,391
12 months or more, Gross unrealized losses	0	71
Total fair value	8,330	7,183
Total gross unrealized losses	29	78
Obligations of U.S. states and municipalities
Available-for-sale securities
Less than 12 months, Fair value	1	1,808
Less than 12 months, Gross unrealized losses	0	15
12 months or more, Fair Value	868	2,477
12 months or more, Gross unrealized losses	9	65
Total fair value	869	4,285
Total gross unrealized losses	9	80
Held-to-maturity securities
Less than 12 months, Fair value	0	12
Less than 12 months, Gross unrealized losses	0	0
12 months or more, Fair value	351	1,114
12 months or more, Gross unrealized losses	1	15
Total fair value	351	1,126
Total gross unrealized losses	1	15
Certificates of deposit
Available-for-sale securities
Less than 12 months, Fair value	75	75
Less than 12 months, Gross unrealized losses	0	0
12 months or more, Fair Value	0	0
12 months or more, Gross unrealized losses	0	0
Total fair value	75	75
Total gross unrealized losses	0	0
Non-U.S. government debt securities
Available-for-sale securities
Less than 12 months, Fair value	2,274	3,123
Less than 12 months, Gross unrealized losses	3	5
12 months or more, Fair Value	1,477	1,937
12 months or more, Gross unrealized losses	6	15
Total fair value	3,751	5,060
Total gross unrealized losses	9	20
Corporate debt securities
Available-for-sale securities
Less than 12 months, Fair value	168	478
Less than 12 months, Gross unrealized losses	1	8
12 months or more, Fair Value	77	37
12 months or more, Gross unrealized losses	2	1
Total fair value	245	515
Total gross unrealized losses	3	9
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Less than 12 months, Fair value	15,862	18,681
Less than 12 months, Gross unrealized losses	81	176
12 months or more, Fair Value	2,725	0
12 months or more, Gross unrealized losses	30	0
Total fair value	18,587	18,681
Total gross unrealized losses	111	176
Asset-backed securities: Other
Available-for-sale securities
Less than 12 months, Fair value	846	1,208
Less than 12 months, Gross unrealized losses	4	6
12 months or more, Fair Value	2,340	2,354
12 months or more, Gross unrealized losses	13	16
Total fair value	3,186	3,562
Total gross unrealized losses	$ 17	$ 22