Investment Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 84,689	$ 94,108
Available for sale, gross unrealized gains	1,018	1,229
Available for sale, gross unrealized losses	399	424
Investment securities available for sale	85,308	94,913
Held to maturity, amortized cost	16,155	17,723
Held to maturity, gross unrealized gains	244	309
Held to maturity, gross unrealized losses	201	190
Held to maturity, fair value	16,198	17,842
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	14,210	20,615
Available for sale, gross unrealized gains	151	218
Available for sale, gross unrealized losses	157	224
Investment securities available for sale	14,204	20,609
Held to maturity, amortized cost	3,092	3,288
Held to maturity, gross unrealized gains	8	7
Held to maturity, gross unrealized losses	4	5
Held to maturity, fair value	3,096	3,290
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	12,777	10,573
Available for sale, gross unrealized gains	127	83
Available for sale, gross unrealized losses	2	1
Investment securities available for sale	12,902	10,655
Held to maturity, amortized cost	5,707	5,114
Held to maturity, gross unrealized gains	2	0
Held to maturity, gross unrealized losses	162	147
Held to maturity, fair value	5,547	4,967
US Treasury and federal agencies, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	19,655	20,648
Available for sale, gross unrealized gains	192	193
Available for sale, gross unrealized losses	129	127
Investment securities available for sale	19,718	20,714
Held to maturity, amortized cost	52	62
Held to maturity, gross unrealized gains	3	4
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	55	66
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	9,159	12,478
Available for sale, gross unrealized gains	73	106
Available for sale, gross unrealized losses	93	124
Investment securities available for sale	9,139	12,460
Held to maturity, amortized cost	1,695	1,814
Held to maturity, gross unrealized gains	3	2
Held to maturity, gross unrealized losses	4	4
Held to maturity, fair value	1,694	1,812
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,599	3,077
Available for sale, gross unrealized gains	0	10
Available for sale, gross unrealized losses	30	34
Investment securities available for sale	1,569	3,053
Held to maturity, amortized cost	897	897
Held to maturity, gross unrealized gains	2	2
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	899	899
Asset-backed securities, sub-prime
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	520	1,005
Available for sale, gross unrealized gains	2	2
Available for sale, gross unrealized losses	31	56
Investment securities available for sale	491	951
Asset-backed securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,932	4,055
Available for sale, gross unrealized gains	76	100
Available for sale, gross unrealized losses	3	10
Investment securities available for sale	3,005	4,145
Held to maturity, amortized cost	500	577
Held to maturity, gross unrealized gains	3	3
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	503	579
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	20,213	21,939
Available for sale, gross unrealized gains	181	241
Available for sale, gross unrealized losses	11	11
Investment securities available for sale	20,383	22,169
Held to maturity, amortized cost	5,403	6,881
Held to maturity, gross unrealized gains	149	191
Held to maturity, gross unrealized losses	23	23
Held to maturity, fair value	5,529	7,049
Non-U.S. debt securities, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	8,210	9,442
Available for sale, gross unrealized gains	125	168
Available for sale, gross unrealized losses	6	4
Investment securities available for sale	8,329	9,606
Held to maturity, amortized cost	3,121	3,787
Held to maturity, gross unrealized gains	140	177
Held to maturity, gross unrealized losses	22	22
Held to maturity, fair value	3,239	3,942
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,926	3,215
Available for sale, gross unrealized gains	7	11
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	2,933	3,226
Held to maturity, amortized cost	2,061	2,868
Held to maturity, gross unrealized gains	9	14
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	2,070	2,881
Government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,993	3,899
Available for sale, gross unrealized gains	10	10
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	4,003	3,909
Held to maturity, amortized cost	153	154
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	153	154
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,084	5,383
Available for sale, gross unrealized gains	39	52
Available for sale, gross unrealized losses	5	7
Investment securities available for sale	5,118	5,428
Held to maturity, amortized cost	68	72
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	1	0
Held to maturity, fair value	67	72
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	10,271	10,532
Available for sale, gross unrealized gains	252	325
Available for sale, gross unrealized losses	74	37
Investment securities available for sale	10,449	10,820
Held to maturity, amortized cost	3	9
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	3	9
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,959	5,280
Available for sale, gross unrealized gains	39	71
Available for sale, gross unrealized losses	14	12
Investment securities available for sale	3,984	5,339
Held to maturity, amortized cost	1,898	2,369
Held to maturity, gross unrealized gains	82	107
Held to maturity, gross unrealized losses	12	15
Held to maturity, fair value	1,968	2,461
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,280	4,033
Available for sale, gross unrealized gains	67	88
Available for sale, gross unrealized losses	11	12
Investment securities available for sale	3,336	4,109
U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	31	29
Available for sale, gross unrealized gains	9	10
Available for sale, gross unrealized losses	1	0
Investment securities available for sale	39	39
Non-U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3	2
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	3	2
U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	282	449
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	282	449
Non-U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	8	8
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	$ 8	8
Federal Family Education Loan Program
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Federal government credit support guarantee, percentage minimum	97.00%
Collateralized Loan Obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	$ 2,900	3,800
Automobile Loan Securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	72	315
Non-US Debt Securities, Covered Bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	3,300	3,300
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	$ 863	$ 1,200