Fair Value Option - Aggregate Differences (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Long-term beneficial interests
Performing loans, ninety days or more past due	$ 0	$ 0
Lending-related commitments, fair value option elected
Long-term beneficial interests
Contractual amount of lending-related commitments	20,900,000,000	18,100,000,000
Contractual lending-related commitments, fair value	75,000,000	(39,000,000)
Contractual principal outstanding
Loans
Nonaccrual loans	4,490,000,000	5,253,000,000
All other performing loans	57,901,000,000	49,939,000,000
Total loans	62,746,000,000	55,520,000,000
Contractual principal outstanding | Principal-protected debt
Long-term debt
Total long-term debt	39,625,000,000	40,560,000,000
Contractual principal outstanding | Loans reported as trading assets
Loans
Nonaccrual loans	3,102,000,000	3,386,000,000
All other performing loans	8,758,000,000	7,917,000,000
Contractual principal outstanding | Loans
Loans
Nonaccrual loans	1,388,000,000	1,867,000,000
90 or more days past due and government guaranteed	355,000,000	328,000,000
All other performing loans	49,143,000,000	42,022,000,000
Fair value
Loans
Nonaccrual loans	1,570,000,000	2,062,000,000
All other performing loans	56,760,000,000	49,089,000,000
Total loans	58,670,000,000	51,468,000,000
Long-term debt
Total long-term debt	75,693,000,000	76,817,000,000
Long-term beneficial interests
Total long-term beneficial interests	193,000,000	41,000,000
Fair value | Principal-protected debt
Long-term debt
Total long-term debt	36,943,000,000	40,526,000,000
Fair value | Nonprincipal-protected debt
Long-term debt
Total long-term debt	38,750,000,000	36,291,000,000
Long-term beneficial interests
Total long-term beneficial interests	193,000,000	41,000,000
Fair value | Loans reported as trading assets
Loans
Nonaccrual loans	426,000,000	555,000,000
All other performing loans	7,477,000,000	6,439,000,000
Fair value | Loans
Loans
Nonaccrual loans	1,144,000,000	1,507,000,000
90 or more days past due and government guaranteed	340,000,000	317,000,000
All other performing loans	49,283,000,000	42,650,000,000
Fair value over/(under) contractual principal outstanding
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(2,920,000,000)	(3,191,000,000)
All other performing loans	(1,141,000,000)	(850,000,000)
Total loans	(4,076,000,000)	(4,052,000,000)
Fair value over/(under) contractual principal outstanding | Principal-protected debt
Long-term debt
Long-term debt, Fair value over/(under) contractual principal outstanding	(2,682,000,000)	(34,000,000)
Fair value over/(under) contractual principal outstanding | Loans reported as trading assets
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(2,676,000,000)	(2,831,000,000)
All other performing loans	(1,281,000,000)	(1,478,000,000)
Fair value over/(under) contractual principal outstanding | Loans
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(244,000,000)	(360,000,000)
90 or more days past due and government guaranteed, Fair value over/(under) contractual principal outstanding	(15,000,000)	(11,000,000)
All other performing loans	$ 140,000,000	$ 628,000,000