Investment Securities - Fair Value and Gross Unrealized Losses by Aging Category (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Available-for-sale securities
Less than 12 months, Fair value	$ 104,435	$ 50,325
Less than 12 months, Gross unrealized losses	547	550
12 months or more, Fair Value	14,385	36,706
12 months or more, Gross unrealized losses	91	993
Total fair value	118,820	87,031
Total gross unrealized losses	638	1,543
Held-to-maturity securities
Less than 12 months, Fair value	2,291	4,397
Less than 12 months, Gross unrealized losses	20	23
12 months or more, Fair value	86	8,196
12 months or more, Gross unrealized losses	0	192
Total fair value	2,377	12,593
Total gross unrealized losses	20	215
Total investment securities with gross unrealized losses
Less than 12 months, Fair value	106,726	54,722
Less than 12 months, Gross unrealized losses	567	573
12 months or more, Fair value	14,471	44,902
12 months or more, Gross unrealized losses	91	1,185
Total fair value	121,197	99,624
Total gross unrealized losses	658	1,758
Total mortgage-backed securities
Available-for-sale securities
Less than 12 months, Fair value	9,304	20,160
Less than 12 months, Gross unrealized losses	41	333
12 months or more, Fair Value	4,147	27,510
12 months or more, Gross unrealized losses	32	825
Total fair value	13,451	47,670
Total gross unrealized losses	73	1,158
Held-to-maturity securities
Less than 12 months, Fair value	2,240	4,385
Less than 12 months, Gross unrealized losses	20	23
12 months or more, Fair value	86	7,082
12 months or more, Gross unrealized losses	0	177
Total fair value	2,326	11,467
Total gross unrealized losses	20	200
U.S. GSEs and government agencies
Available-for-sale securities
Less than 12 months, Fair value	8,505	17,656
Less than 12 months, Gross unrealized losses	37	318
12 months or more, Fair Value	2,952	22,728
12 months or more, Gross unrealized losses	24	656
Total fair value	11,457	40,384
Total gross unrealized losses	61	974
Held-to-maturity securities
Less than 12 months, Fair value	2,240	4,385
Less than 12 months, Gross unrealized losses	20	23
12 months or more, Fair value	86	7,082
12 months or more, Gross unrealized losses	0	177
Total fair value	2,326	11,467
Total gross unrealized losses	20	200
Residential: U.S.
Available-for-sale securities
Less than 12 months, Fair value	0	623
Less than 12 months, Gross unrealized losses	0	4
12 months or more, Fair Value	558	1,445
12 months or more, Gross unrealized losses	6	27
Total fair value	558	2,068
Total gross unrealized losses	6	31
Residential: Non-U.S.
Available-for-sale securities
Less than 12 months, Fair value	47	907
Less than 12 months, Gross unrealized losses	0	5
12 months or more, Fair Value	472	165
12 months or more, Gross unrealized losses	2	1
Total fair value	519	1,072
Total gross unrealized losses	2	6
Commercial
Available-for-sale securities
Less than 12 months, Fair value	752	974
Less than 12 months, Gross unrealized losses	4	6
12 months or more, Fair Value	165	3,172
12 months or more, Gross unrealized losses	0	141
Total fair value	917	4,146
Total gross unrealized losses	4	147
U.S. Treasury and government agencies
Available-for-sale securities
Less than 12 months, Fair value	84,152	4,792
Less than 12 months, Gross unrealized losses	489	7
12 months or more, Fair Value	540	2,391
12 months or more, Gross unrealized losses	4	71
Total fair value	84,692	7,183
Total gross unrealized losses	493	78
Held-to-maturity securities
Less than 12 months, Fair value	51	0
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	51	0
Total gross unrealized losses	0	0
Obligations of U.S. states and municipalities
Available-for-sale securities
Less than 12 months, Fair value	41	1,808
Less than 12 months, Gross unrealized losses	0	15
12 months or more, Fair Value	23	2,477
12 months or more, Gross unrealized losses	0	65
Total fair value	64	4,285
Total gross unrealized losses	0	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	0	1,114
12 months or more, Gross unrealized losses	0	15
Total fair value	0	1,126
Total gross unrealized losses	0	15
Certificates of deposit
Available-for-sale securities
Less than 12 months, Fair value	74	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	74	75
Total gross unrealized losses	0	0
Non-U.S. government debt securities
Available-for-sale securities
Less than 12 months, Fair value	3,189	3,123
Less than 12 months, Gross unrealized losses	6	5
12 months or more, Fair Value	1,357	1,937
12 months or more, Gross unrealized losses	4	15
Total fair value	4,546	5,060
Total gross unrealized losses	10	20
Corporate debt securities
Available-for-sale securities
Less than 12 months, Fair value	83	478
Less than 12 months, Gross unrealized losses	0	8
12 months or more, Fair Value	36	37
12 months or more, Gross unrealized losses	1	1
Total fair value	119	515
Total gross unrealized losses	1	9
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Less than 12 months, Fair value	7,086	18,681
Less than 12 months, Gross unrealized losses	8	176
12 months or more, Fair Value	6,684	0
12 months or more, Gross unrealized losses	44	0
Total fair value	13,770	18,681
Total gross unrealized losses	52	176
Asset-backed securities: Other
Available-for-sale securities
Less than 12 months, Fair value	506	1,208
Less than 12 months, Gross unrealized losses	3	6
12 months or more, Fair Value	1,598	2,354
12 months or more, Gross unrealized losses	6	16
Total fair value	2,104	3,562
Total gross unrealized losses	$ 9	$ 22