Commitments, Contingencies and Guarantees - Guarantees (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivative Guarantee [Member]
Guarantor Obligations [Line Items]
Carrying Value of Net Liability	$ 5,897	$ 3,817
Maximum Payout/Notional Amount by Period of Expiration	194,783	224,201
Derivative Guarantee [Member] | Maturities, Remainder of Year 1 [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration	22,573
Derivative Guarantee [Member] | Maturities, Year 1 [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration		91,814
Derivative Guarantee [Member] | Maturities, Year 2 and Year 3 [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration	102,509	76,693
Derivative Guarantee [Member] | Maturities, Year 4 and Year 5 [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration	31,521	19,377
Derivative Guarantee [Member] | Maturities, Year 6 and Thereafter [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration	38,180	36,317
Securities Lending Indemnification [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration	20,901	17,891
Securities Lending Indemnification [Member] | Maturities, Remainder of Year 1 [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration	20,901
Securities Lending Indemnification [Member] | Maturities, Year 1 [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration		17,891
Financial Guarantee [Member]
Guarantor Obligations [Line Items]
Carrying Value of Net Liability	256	27
Maximum Payout/Notional Amount by Period of Expiration	7,890	6,126
Financial Guarantee [Member] | Maturities, Remainder of Year 1 [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration	558
Financial Guarantee [Member] | Maturities, Year 1 [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration		2,044
Financial Guarantee [Member] | Maturities, Year 2 and Year 3 [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration	2,106	1,714
Financial Guarantee [Member] | Maturities, Year 4 and Year 5 [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration	3,171	2,219
Financial Guarantee [Member] | Maturities, Year 6 and Thereafter [Member]
Guarantor Obligations [Line Items]
Maximum Payout/Notional Amount by Period of Expiration	$ 2,055	$ 149