Fair Value Option - Aggregate Differences (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
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	18,100,000,000	8,600,000,000
Other guarantees and commitments, Carrying value	(39,000,000)	(120,000,000)
Contractual principal outstanding
Loans
Nonaccrual loans	5,253,000,000	3,527,000,000
90 or more days past due and government guaranteed	328,000,000	138,000,000
All other performing loans	49,939,000,000	52,243,000,000
Total loans	55,520,000,000	55,908,000,000
Contractual principal outstanding | Principal-protected debt
Long-term debt
Total long-term debt	40,560,000,000	40,124,000,000
Contractual principal outstanding | Loans reported as trading assets
Loans
Nonaccrual loans	3,386,000,000	2,563,000,000
90 or more days past due and government guaranteed	0	0
All other performing loans	7,917,000,000	8,288,000,000
Contractual principal outstanding | Loans
Loans
Nonaccrual loans	1,867,000,000	964,000,000
90 or more days past due and government guaranteed	328,000,000	138,000,000
All other performing loans	42,022,000,000	43,955,000,000
Fair value
Loans
Nonaccrual loans	2,062,000,000	930,000,000
90 or more days past due and government guaranteed	317,000,000	129,000,000
All other performing loans	49,089,000,000	50,909,000,000
Total loans	51,468,000,000	51,968,000,000
Long-term debt
Total long-term debt	76,817,000,000	75,745,000,000
Long-term beneficial interests
Total long-term beneficial interests	41,000,000	36,000,000
Fair value | Principal-protected debt
Long-term debt
Total long-term debt	40,526,000,000	39,246,000,000
Fair value | Nonprincipal-protected debt
Long-term debt
Total long-term debt	36,291,000,000	36,499,000,000
Long-term beneficial interests
Total long-term beneficial interests	41,000,000	36,000,000
Fair value | Loans reported as trading assets
Loans
Nonaccrual loans	555,000,000	234,000,000
90 or more days past due and government guaranteed	0	0
All other performing loans	6,439,000,000	6,779,000,000
Fair value | Loans
Loans
Nonaccrual loans	1,507,000,000	696,000,000
90 or more days past due and government guaranteed	317,000,000	129,000,000
All other performing loans	42,650,000,000	44,130,000,000
Fair value over/(under) contractual principal outstanding
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(3,191,000,000)	(2,597,000,000)
90 or more days past due and government guaranteed, Fair value over/(under) contractual principal outstanding	(11,000,000)	(9,000,000)
All other performing loans	(850,000,000)	(1,334,000,000)
Total loans	(4,052,000,000)	(3,940,000,000)
Fair value over/(under) contractual principal outstanding | Principal-protected debt
Long-term debt
Long-term debt, Fair value over/(under) contractual principal outstanding	(34,000,000)	(878,000,000)
Fair value over/(under) contractual principal outstanding | Loans reported as trading assets
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(2,831,000,000)	(2,329,000,000)
90 or more days past due and government guaranteed, Fair value over/(under) contractual principal outstanding	0	0
All other performing loans	(1,478,000,000)	(1,509,000,000)
Fair value over/(under) contractual principal outstanding | Loans
Loans
Nonaccrual loans, Fair value over/(under) contractual principal outstanding	(360,000,000)	(268,000,000)
90 or more days past due and government guaranteed, Fair value over/(under) contractual principal outstanding	(11,000,000)	(9,000,000)
All other performing loans	$ 628,000,000	$ 175,000,000