Fair Value Option - Aggregate differences (Details) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
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	5,674,000,000	5,580,000,000
Contractual letters of credit, fair value	(88,000,000)	(94,000,000)
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	4,600,000,000
Contractual letters of credit, fair value	88,000,000	94,000,000
Contractual principal outstanding
Loans
Nonaccrual loans	3,490,000,000	3,491,000,000
Total loans	36,669,000,000	37,042,000,000
Contractual principal outstanding | Loans reported as trading assets
Loans
Nonaccrual loans	3,483,000,000	3,484,000,000
All other performing loans	31,294,000,000	30,780,000,000
Contractual principal outstanding | Loans
Loans
Nonaccrual loans	7,000,000	7,000,000
All other performing loans	1,885,000,000	2,771,000,000
Contractual principal outstanding | Principal-protected debt
Long-term debt
Long-term debt	19,129,000,000	17,910,000,000
Fair value
Loans
Nonaccrual loans	770,000,000	638,000,000
Total loans	31,258,000,000	31,574,000,000
Long-term debt
Long-term debt	35,215,000,000	33,065,000,000
Long-term beneficial interests
Long-term beneficial interests	670,000,000	787,000,000
Fair value | Loans reported as trading assets
Loans
Nonaccrual loans	763,000,000	631,000,000
All other performing loans	28,609,000,000	28,184,000,000
Fair value | Loans
Loans
Nonaccrual loans	7,000,000	7,000,000
All other performing loans	1,879,000,000	2,752,000,000
Fair value | Principal-protected debt
Long-term debt
Long-term debt	17,987,000,000	16,611,000,000
Fair value | Nonprincipal-protected debt
Long-term debt
Long-term debt	17,228,000,000	16,454,000,000
Long-term beneficial interests
Long-term beneficial interests	670,000,000	787,000,000
Fair value over/(under) contractual principal outstanding
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(2,720,000,000)	(2,853,000,000)
Total loans	(5,411,000,000)	(5,468,000,000)
Fair value over/(under) contractual principal outstanding | Loans reported as trading assets
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(2,720,000,000)	(2,853,000,000)
All other performing loans	(2,685,000,000)	(2,596,000,000)
Fair value over/(under) contractual principal outstanding | Loans
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	0	0
All other performing loans	(6,000,000)	(19,000,000)
Fair value over/(under) contractual principal outstanding | Principal-protected debt
Long-term debt
Long-term debt	$ (1,142,000,000)	$ (1,299,000,000)