Fair Value Option - Aggregate differences (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Long-term beneficial interests
Performing loans - 90 days or more outstanding	$ 0	$ 0
Other guarantees and commitments
Long-term beneficial interests
Other guarantees and commitments, contractual amount	5,984,000,000	5,720,000,000
Guarantor obligations, current carrying value	(107,000,000)	(121,000,000)
Letters of credit hedged by derivative transactions | Other guarantees and commitments
Long-term beneficial interests
Other guarantees and commitments, contractual amount	4,400,000,000	4,500,000,000
Guarantor obligations, current carrying value	(130,000,000)	(147,000,000)
Carrying value
Loans
Nonaccrual loans	4,103,000,000	3,854,000,000
Total loans	41,099,000,000	43,859,000,000
Carrying value | Trading assets
Loans
Nonaccrual loans	4,096,000,000	3,847,000,000
All other performing loans	34,729,000,000	37,608,000,000
Carrying value | Loans
Loans
Nonaccrual loans	7,000,000	7,000,000
All other performing loans	2,267,000,000	2,397,000,000
Carrying value | Principal-protected debt
Long-term debt
Long-term debt	14,747,000,000	14,660,000,000
Estimate of Fair Value
Loans
Nonaccrual loans	1,104,000,000	912,000,000
Total loans	36,251,000,000	38,763,000,000
Long-term debt
Long-term debt	31,316,000,000	30,226,000,000
Long-term beneficial interests
Total long-term beneficial interests	1,330,000,000	2,162,000,000
Estimate of Fair Value | Trading assets
Loans
Nonaccrual loans	1,097,000,000	905,000,000
All other performing loans	32,885,000,000	35,462,000,000
Estimate of Fair Value | Loans
Loans
Nonaccrual loans	7,000,000	7,000,000
All other performing loans	2,262,000,000	2,389,000,000
Estimate of Fair Value | Principal-protected debt
Long-term debt
Long-term debt	14,690,000,000	15,484,000,000
Estimate of Fair Value | Nonprincipal-protected debt
Long-term debt
Long-term debt	16,626,000,000	14,742,000,000
Long-term beneficial interests
Total long-term beneficial interests	1,330,000,000	2,162,000,000
Change During Period
Loans
Nonaccrual loans	(2,999,000,000)	(2,942,000,000)
Total loans	(4,848,000,000)	(5,096,000,000)
Change During Period | Trading assets
Loans
Nonaccrual loans	(2,999,000,000)	(2,942,000,000)
All other performing loans	(1,844,000,000)	(2,146,000,000)
Change During Period | Loans
Loans
Nonaccrual loans	0	0
All other performing loans	(5,000,000)	(8,000,000)
Change During Period | Principal-protected debt
Long-term debt
Long-term debt	$ (57,000,000)	$ 824,000,000