Securities - Amortized Costs, Fair Value (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Available-for-sale Debt Securities:
Amortized cost	$ 271,608	$ 288,466
Gross unrealized gains	8,230	8,143
Gross unrealized losses	291	387
Fair value	279,547	296,222
Available-for-sale Equity Securities:
Amortized cost	2,309	2,513
Gross unrealized gains	16	17
Gross unrealized losses	0	0
Fair value	2,325	2,530
Available-for-sale Securities:
Amortized cost	273,917	290,979
Gross unrealized gains	8,246	8,160
Gross unrealized losses	291	387
Fair value	281,872	298,752
Held-to-maturity Securities:
Amortized cost	49,264	49,252
Gross unrealized gains	2,118	1,902
Gross unrealized losses	12	0
Fair value	51,370	51,154
Mortgage-backed securities
Available-for-sale Debt Securities:
Amortized cost	126,943	133,598
Gross unrealized gains	3,909	3,842
Gross unrealized losses	87	118
Fair value	130,765	137,322
Mortgage-backed securities, U.S. government agencies
Available-for-sale Debt Securities:
Amortized cost	63,165	63,089
Gross unrealized gains	2,443	2,302
Gross unrealized losses	52	72
Fair value	65,556	65,319
Mortgage-backed securities, Commercial
Available-for-sale Debt Securities:
Amortized cost	22,157	20,687
Gross unrealized gains	461	438
Gross unrealized losses	12	17
Fair value	22,606	21,108
U.S. Treasury and government agencies
Available-for-sale Debt Securities:
Amortized cost	11,952	13,603
Gross unrealized gains	29	56
Gross unrealized losses	16	14
Fair value	11,965	13,645
Obligations of U.S. states and municipalities
Available-for-sale Debt Securities:
Amortized cost	28,922	27,841
Gross unrealized gains	2,302	2,243
Gross unrealized losses	25	16
Fair value	31,199	30,068
Held-to-maturity Securities:
Amortized cost	11,600	10,200
Certificates of deposit
Available-for-sale Debt Securities:
Amortized cost	1,021	1,103
Gross unrealized gains	3	1
Gross unrealized losses	1	1
Fair value	1,023	1,103
Non-U.S. government debt securities
Available-for-sale Debt Securities:
Amortized cost	44,543	51,492
Gross unrealized gains	1,330	1,272
Gross unrealized losses	16	21
Fair value	45,857	52,743
Corporate debt securities
Available-for-sale Debt Securities:
Amortized cost	16,850	18,158
Gross unrealized gains	369	398
Gross unrealized losses	28	24
Fair value	17,191	18,532
Asset-backed securities, Collateralized loan obligations
Available-for-sale Debt Securities:
Amortized cost	29,664	30,229
Gross unrealized gains	131	147
Gross unrealized losses	112	182
Fair value	29,683	30,194
Asset-backed securities, Other
Available-for-sale Debt Securities:
Amortized cost	11,713	12,442
Gross unrealized gains	157	184
Gross unrealized losses	6	11
Fair value	11,864	12,615
US government-sponsored and enterprises obligations
Available-for-sale Securities:
Fair value	55,000	59,300
Held-to-maturity Securities:
Amortized cost	34,200	35,300
US Government Corporations and Agencies
Held-to-maturity Securities:
Amortized cost	3,400	3,700
Residential mortgage-backed securities | Residential mortgage-backed securities, Prime and Alt-A
Available-for-sale Debt Securities:
Amortized cost	6,433	5,595
Gross unrealized gains	83	78
Gross unrealized losses	22	29
Fair value	6,494	5,644
Residential mortgage-backed securities | Residential mortgage-backed securities, Subprime
Available-for-sale Debt Securities:
Amortized cost	633	677
Gross unrealized gains	13	14
Gross unrealized losses	0	0
Fair value	646	691
Residential mortgage-backed securities | Residential mortgage-backed securities, Non-U.S.
Available-for-sale Debt Securities:
Amortized cost	34,555	43,550
Gross unrealized gains	909	1,010
Gross unrealized losses	1	0
Fair value	$ 35,463	$ 44,560