Fair Value Option - Aggregate differences (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Long-term beneficial interests
Performing loans, ninety days or more past due	$ 0	$ 0
Other guarantees and commitments
Long-term beneficial interests
Contractual amount of letters of credit	5,580,000,000	5,720,000,000
Contractual letters of credit, fair value	94,000,000	121,000,000
Letters of credit which fair value option was elected | Other guarantees and commitments
Long-term beneficial interests
Contractual amount of letters of credit	4,600,000,000	4,500,000,000
Contractual letters of credit, fair value	(94,000,000)	(147,000,000)
Carrying value
Loans
Nonaccrual loans	3,491,000,000	3,854,000,000
Total loans	37,042,000,000	43,859,000,000
Carrying value | Trading assets
Loans
Nonaccrual loans	3,484,000,000	3,847,000,000
All other performing loans	30,780,000,000	37,608,000,000
Carrying value | Loans
Loans
Nonaccrual loans	7,000,000	7,000,000
All other performing loans	2,771,000,000	2,397,000,000
Carrying value | Principal-protected debt
Long-term debt
Long-term debt	17,910,000,000	14,660,000,000
Estimate of Fair Value
Loans
Nonaccrual loans	638,000,000	912,000,000
Total loans	31,574,000,000	38,763,000,000
Long-term debt
Long-term debt	33,065,000,000	30,226,000,000
Long-term beneficial interests
Long-term beneficial interests	787,000,000	2,162,000,000
Estimate of Fair Value | Trading assets
Loans
Nonaccrual loans	631,000,000	905,000,000
All other performing loans	28,184,000,000	35,462,000,000
Estimate of Fair Value | Loans
Loans
Nonaccrual loans	7,000,000	7,000,000
All other performing loans	2,752,000,000	2,389,000,000
Estimate of Fair Value | Principal-protected debt
Long-term debt
Long-term debt	16,611,000,000	15,484,000,000
Estimate of Fair Value | Nonprincipal-protected debt
Long-term debt
Long-term debt	16,454,000,000	14,742,000,000
Long-term beneficial interests
Long-term beneficial interests	787,000,000	2,162,000,000
Change During Period
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(2,853,000,000)	(2,942,000,000)
Total loans	(5,468,000,000)	(5,096,000,000)
Change During Period | Trading assets
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(2,853,000,000)	(2,942,000,000)
All other performing loans	(2,596,000,000)	(2,146,000,000)
Change During Period | Loans
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	0	0
All other performing loans	(19,000,000)	(8,000,000)
Change During Period | Principal-protected debt
Long-term debt
Long-term debt	$ (1,299,000,000)	$ 824,000,000