Securities - Continuous Unrealized Loss Position (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Held-to-maturity Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	$ 12,994	$ 3,763
Less than 12 months, Gross unrealized losses	276	46
12 months or more, Fair value	441	0
12 months or more, Gross unrealized losses	15	0
Total fair value	13,435	3,763
Total gross unrealized losses	291	46
Total Securities with Gross Unrealized Losses
Less than 12 months, Fair value	84,047	76,475
Less than 12 months, Gross unrealized losses	1,785	905
12 months or more, Fair value	12,544	14,877
12 months or more, Gross unrealized losses	153	251
Total fair value	96,591	91,352
Total gross unrealized losses	1,938	1,156
Debt securities
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	71,053	72,712
Less than 12 months, Gross unrealized losses	1,509	859
12 months or more, Fair Value	12,103	14,877
12 months or more, Gross unrealized losses	138	251
Total fair value	83,156	87,589
Total gross unrealized losses	1,647	1,110
Total mortgage-backed securities
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	33,557	33,949
Less than 12 months, Gross unrealized losses	486	397
12 months or more, Fair Value	3,543	1,760
12 months or more, Gross unrealized losses	43	22
Total fair value	37,100	35,709
Total gross unrealized losses	529	419
Held-to-maturity Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	8,292	3,294
Less than 12 months, Gross unrealized losses	151	42
12 months or more, Fair value	441	0
12 months or more, Gross unrealized losses	15	0
Total fair value	8,733	3,294
Total gross unrealized losses	166	42
U.S. government agencies
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	29,856	13,002
Less than 12 months, Gross unrealized losses	463	95
12 months or more, Fair Value	506	697
12 months or more, Gross unrealized losses	11	11
Total fair value	30,362	13,699
Total gross unrealized losses	474	106
Held-to-maturity Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	3,129	3,294
Less than 12 months, Gross unrealized losses	37	42
12 months or more, Fair value	0	0
12 months or more, Gross unrealized losses	0	0
Total fair value	3,129	3,294
Total gross unrealized losses	37	42
Residential: Prime and Alt-A | Residential mortgage-backed securities
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	977	4,455
Less than 12 months, Gross unrealized losses	2	43
12 months or more, Fair Value	1,018	238
12 months or more, Gross unrealized losses	20	6
Total fair value	1,995	4,693
Total gross unrealized losses	22	49
Residential: Subprime | Residential mortgage-backed securities
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	396	692
Less than 12 months, Gross unrealized losses	4	8
12 months or more, Fair Value	55	0
12 months or more, Gross unrealized losses	2	0
Total fair value	451	692
Total gross unrealized losses	6	8
Residential: Non-U.S. | Residential mortgage-backed securities
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	0	2,021
Less than 12 months, Gross unrealized losses	0	12
12 months or more, Fair Value	886	167
12 months or more, Gross unrealized losses	7	1
Total fair value	886	2,188
Total gross unrealized losses	7	13
Commercial
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	2,328	13,779
Less than 12 months, Gross unrealized losses	17	239
12 months or more, Fair Value	1,078	658
12 months or more, Gross unrealized losses	3	4
Total fair value	3,406	14,437
Total gross unrealized losses	20	243
Held-to-maturity Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	5,163	0
Less than 12 months, Gross unrealized losses	114	0
12 months or more, Fair value	441	0
12 months or more, Gross unrealized losses	15	0
Total fair value	5,604	0
Total gross unrealized losses	129	0
U.S. Treasury and government agencies
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	23,543	10,998
Less than 12 months, Gross unrealized losses	796	166
12 months or more, Fair Value	0	0
12 months or more, Gross unrealized losses	0	0
Total fair value	23,543	10,998
Total gross unrealized losses	796	166
Obligations of U.S. states and municipalities
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	7,215	1,676
Less than 12 months, Gross unrealized losses	181	18
12 months or more, Fair Value	55	205
12 months or more, Gross unrealized losses	3	5
Total fair value	7,270	1,881
Total gross unrealized losses	184	23
Held-to-maturity Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	4,702	469
Less than 12 months, Gross unrealized losses	125	4
12 months or more, Fair value	0	0
12 months or more, Gross unrealized losses	0	0
Total fair value	4,702	469
Total gross unrealized losses	125	4
Certificates of deposit
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	0	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	0	0
Total gross unrealized losses	0	0
Non-U.S. government debt securities
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	4,436	3,267
Less than 12 months, Gross unrealized losses	36	26
12 months or more, Fair Value	421	367
12 months or more, Gross unrealized losses	9	15
Total fair value	4,857	3,634
Total gross unrealized losses	45	41
Corporate debt securities
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	797	3,198
Less than 12 months, Gross unrealized losses	2	125
12 months or more, Fair Value	829	848
12 months or more, Gross unrealized losses	20	45
Total fair value	1,626	4,046
Total gross unrealized losses	22	170
Asset-backed securities: Collateralized loan obligations
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	766	15,340
Less than 12 months, Gross unrealized losses	2	67
12 months or more, Fair Value	5,263	10,692
12 months or more, Gross unrealized losses	24	124
Total fair value	6,029	26,032
Total gross unrealized losses	26	191
Asset-backed securities: Other
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	739	4,284
Less than 12 months, Gross unrealized losses	6	60
12 months or more, Fair Value	1,992	1,005
12 months or more, Gross unrealized losses	39	40
Total fair value	2,731	5,289
Total gross unrealized losses	45	100
Available-for-sale equity securities
Available-for-sale Securities, Securities with Gross Unrealized Losses:
Less than 12 months, Fair value	0	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	0	0
Total gross unrealized losses	$ 0	$ 0