Securities - Amortized Costs, Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Fair value of securities transferred from available-for-sale to held-to-maturity			$ 19,300
Net pre-tax unrealized losses in AOCI on securities on the date of transfer			$ (9)
Available-for-sale Debt Securities:
Amortized cost	$ 235,391	$ 288,466
Gross unrealized gains	5,386	8,143
Gross unrealized losses	1,110	387
Fair value	239,667	296,222
Available-for-sale Equity Securities:
Amortized cost	2,067	2,513
Gross unrealized gains	20	17
Gross unrealized losses	0	0
Fair value	2,087	2,530
Available-for-sale Securities:
Amortized cost	237,458	290,979
Gross unrealized gains	5,406	8,160
Gross unrealized losses	1,110	387
Fair value	241,754	298,752
Held-to-maturity Securities:
Amortized cost	49,073	49,252
Gross unrealized gains	1,560	1,902
Gross unrealized losses	46	0
Fair value	50,587	51,154
Total mortgage-backed securities
Available-for-sale Debt Securities:
Amortized cost	103,980	133,598
Gross unrealized gains	2,021	3,842
Gross unrealized losses	419	118
Fair value	105,582	137,322
U.S. government agencies
Available-for-sale Debt Securities:
Amortized cost	53,689	63,089
Gross unrealized gains	1,483	2,302
Gross unrealized losses	106	72
Fair value	55,066	65,319
Residential: Prime and Alt-A | Residential mortgage-backed securities
Available-for-sale Debt Securities:
Amortized cost	7,462	5,595
Gross unrealized gains	40	78
Gross unrealized losses	57	29
Fair value	7,445	5,644
Residential: Subprime | Residential mortgage-backed securities
Available-for-sale Debt Securities:
Amortized cost	210	677
Gross unrealized gains	7	14
Gross unrealized losses	0	0
Fair value	217	691
Residential: Non-U.S. | Residential mortgage-backed securities
Available-for-sale Debt Securities:
Amortized cost	19,629	43,550
Gross unrealized gains	341	1,010
Gross unrealized losses	13	0
Fair value	19,957	44,560
Commercial
Available-for-sale Debt Securities:
Amortized cost	22,990	20,687
Gross unrealized gains	150	438
Gross unrealized losses	243	17
Fair value	22,897	21,108
U.S. Treasury and government agencies
Available-for-sale Debt Securities:
Amortized cost	11,202	13,603
Gross unrealized gains	0	56
Gross unrealized losses	166	14
Fair value	11,036	13,645
Obligations of U.S. states and municipalities
Available-for-sale Debt Securities:
Amortized cost	31,328	27,841
Gross unrealized gains	2,245	2,243
Gross unrealized losses	23	16
Fair value	33,550	30,068
Held-to-maturity Securities:
Amortized cost	12,800	10,200
Certificates of deposit
Available-for-sale Debt Securities:
Amortized cost	282	1,103
Gross unrealized gains	1	1
Gross unrealized losses	0	1
Fair value	283	1,103
Non-U.S. government debt securities
Available-for-sale Debt Securities:
Amortized cost	35,864	51,492
Gross unrealized gains	853	1,272
Gross unrealized losses	41	21
Fair value	36,676	52,743
Corporate debt securities
Available-for-sale Debt Securities:
Amortized cost	12,464	18,158
Gross unrealized gains	142	398
Gross unrealized losses	170	24
Fair value	12,436	18,532
Asset-backed securities: Collateralized loan obligations
Available-for-sale Debt Securities:
Amortized cost	31,146	30,229
Gross unrealized gains	52	147
Gross unrealized losses	191	182
Fair value	31,007	30,194
Asset-backed securities: Other
Available-for-sale Debt Securities:
Amortized cost	9,125	12,442
Gross unrealized gains	72	184
Gross unrealized losses	100	11
Fair value	9,097	12,615
US government-sponsored and enterprises obligations
Available-for-sale Securities:
Fair value	42,300	59,300
Held-to-maturity Securities:
Amortized cost	30,800	35,300
US Government agencies
Held-to-maturity Securities:
Amortized cost	$ 5,500	$ 3,700