Investment Securities - Schedule of Marketable Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	$ 69,843,000,000	$ 94,108,000,000
Available for sale, gross unrealized gains	735,000,000	1,229,000,000
Available for sale, gross unrealized losses	508,000,000	424,000,000
Investment securities available for sale	70,070,000,000	94,913,000,000
Held to maturity, amortized cost	29,952,000,000	17,723,000,000
Held to maturity, gross unrealized gains	179,000,000	309,000,000
Held to maturity, gross unrealized losses	333,000,000	190,000,000
Held to maturity, fair value	29,798,000,000	17,842,000,000
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,717,000,000	10,573,000,000
Available for sale, gross unrealized gains	6,000,000	83,000,000
Available for sale, gross unrealized losses	5,000,000	1,000,000
Investment securities available for sale	5,718,000,000	10,655,000,000
Held to maturity, amortized cost	20,878,000,000	5,114,000,000
Held to maturity, gross unrealized gains	2,000,000	0
Held to maturity, gross unrealized losses	217,000,000	147,000,000
Held to maturity, fair value	20,663,000,000	4,967,000,000
US Treasury and federal agencies, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	18,168,000,000	20,648,000,000
Available for sale, gross unrealized gains	131,000,000	193,000,000
Available for sale, gross unrealized losses	134,000,000	127,000,000
Investment securities available for sale	18,165,000,000	20,714,000,000
Held to maturity, amortized cost	610,000,000	62,000,000
Held to maturity, gross unrealized gains	2,000,000	4,000,000
Held to maturity, gross unrealized losses	8,000,000	0
Held to maturity, fair value	604,000,000	66,000,000
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	7,358,000,000	12,478,000,000
Available for sale, gross unrealized gains	16,000,000	106,000,000
Available for sale, gross unrealized losses	198,000,000	124,000,000
Investment securities available for sale	7,176,000,000	12,460,000,000
Held to maturity, amortized cost	1,592,000,000	1,814,000,000
Held to maturity, gross unrealized gains	0	2,000,000
Held to maturity, gross unrealized losses	47,000,000	4,000,000
Held to maturity, fair value	1,545,000,000	1,812,000,000
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,378,000,000	3,077,000,000
Available for sale, gross unrealized gains	0	10,000,000
Available for sale, gross unrealized losses	37,000,000	34,000,000
Investment securities available for sale	1,341,000,000	3,053,000,000
Held to maturity, amortized cost	897,000,000	897,000,000
Held to maturity, gross unrealized gains	0	2,000,000
Held to maturity, gross unrealized losses	1,000,000	0
Held to maturity, fair value	896,000,000	899,000,000
Asset-backed securities, sub-prime
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	448,000,000	1,005,000,000
Available for sale, gross unrealized gains	2,000,000	2,000,000
Available for sale, gross unrealized losses	31,000,000	56,000,000
Investment securities available for sale	419,000,000	951,000,000
Asset-backed securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	1,724,000,000	4,055,000,000
Available for sale, gross unrealized gains	43,000,000	100,000,000
Available for sale, gross unrealized losses	3,000,000	10,000,000
Investment securities available for sale	1,764,000,000	4,145,000,000
Held to maturity, amortized cost	366,000,000	577,000,000
Held to maturity, gross unrealized gains	2,000,000	3,000,000
Held to maturity, gross unrealized losses	1,000,000	1,000,000
Held to maturity, fair value	367,000,000	579,000,000
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	10,908,000,000	20,615,000,000
Available for sale, gross unrealized gains	61,000,000	218,000,000
Available for sale, gross unrealized losses	269,000,000	224,000,000
Investment securities available for sale	10,700,000,000	20,609,000,000
Held to maturity, amortized cost	2,855,000,000	3,288,000,000
Held to maturity, gross unrealized gains	2,000,000	7,000,000
Held to maturity, gross unrealized losses	49,000,000	5,000,000
Held to maturity, fair value	2,808,000,000	3,290,000,000
Non-U.S. debt securities, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	7,010,000,000	9,442,000,000
Available for sale, gross unrealized gains	72,000,000	168,000,000
Available for sale, gross unrealized losses	11,000,000	4,000,000
Investment securities available for sale	7,071,000,000	9,606,000,000
Held to maturity, amortized cost	2,202,000,000	3,787,000,000
Held to maturity, gross unrealized gains	109,000,000	177,000,000
Held to maturity, gross unrealized losses	26,000,000	22,000,000
Held to maturity, fair value	2,285,000,000	3,942,000,000
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,272,000,000	3,215,000,000
Available for sale, gross unrealized gains	2,000,000	11,000,000
Available for sale, gross unrealized losses	7,000,000	0
Investment securities available for sale	3,267,000,000	3,226,000,000
Held to maturity, amortized cost	1,415,000,000	2,868,000,000
Held to maturity, gross unrealized gains	4,000,000	14,000,000
Held to maturity, gross unrealized losses	3,000,000	1,000,000
Held to maturity, fair value	1,416,000,000	2,881,000,000
Government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	4,348,000,000	3,899,000,000
Available for sale, gross unrealized gains	7,000,000	10,000,000
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	4,355,000,000	3,909,000,000
Held to maturity, amortized cost	239,000,000	154,000,000
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	1,000,000	0
Held to maturity, fair value	238,000,000	154,000,000
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	4,817,000,000	5,383,000,000
Available for sale, gross unrealized gains	29,000,000	52,000,000
Available for sale, gross unrealized losses	12,000,000	7,000,000
Investment securities available for sale	4,834,000,000	5,428,000,000
Held to maturity, amortized cost	65,000,000	72,000,000
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	65,000,000	72,000,000
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	19,447,000,000	21,939,000,000
Available for sale, gross unrealized gains	110,000,000	241,000,000
Available for sale, gross unrealized losses	30,000,000	11,000,000
Investment securities available for sale	19,527,000,000	22,169,000,000
Held to maturity, amortized cost	3,921,000,000	6,881,000,000
Held to maturity, gross unrealized gains	113,000,000	191,000,000
Held to maturity, gross unrealized losses	30,000,000	23,000,000
Held to maturity, fair value	4,004,000,000	7,049,000,000
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	9,402,000,000	10,532,000,000
Available for sale, gross unrealized gains	371,000,000	325,000,000
Available for sale, gross unrealized losses	27,000,000	37,000,000
Investment securities available for sale	9,746,000,000	10,820,000,000
Held to maturity, amortized cost	1,000,000	9,000,000
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	1,000,000	9,000,000
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,993,000,000	5,280,000,000
Available for sale, gross unrealized gains	16,000,000	71,000,000
Available for sale, gross unrealized losses	22,000,000	12,000,000
Investment securities available for sale	2,987,000,000	5,339,000,000
Held to maturity, amortized cost	1,687,000,000	2,369,000,000
Held to maturity, gross unrealized gains	60,000,000	107,000,000
Held to maturity, gross unrealized losses	29,000,000	15,000,000
Held to maturity, fair value	1,718,000,000	2,461,000,000
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,611,000,000	4,033,000,000
Available for sale, gross unrealized gains	31,000,000	88,000,000
Available for sale, gross unrealized losses	18,000,000	12,000,000
Investment securities available for sale	2,624,000,000	4,109,000,000
U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	33,000,000	29,000,000
Available for sale, gross unrealized gains	9,000,000	10,000,000
Available for sale, gross unrealized losses	3,000,000	0
Investment securities available for sale	39,000,000	39,000,000
Non-U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,000,000	2,000,000
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	3,000,000	2,000,000
U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	542,000,000	449,000,000
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	542,000,000	449,000,000
Non-U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	19,000,000	8,000,000
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	$ 19,000,000	8,000,000
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	$ 1,760,000,000	3,800,000,000
Automobile loan securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	0	315,000,000
Non-US debt securities, covered bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	3,180,000,000	3,300,000,000
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	$ 613,000,000	$ 1,200,000,000