Derivatives and Hedging Activities - Outstanding Interest Rate Swaptions and Derivative Instrument Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2018	$ 14,609,961
Additions	30,677,397
Settlement, Termination, Expiration or Exercise	(30,799,281)
Notional Amount as of December 31, 2019	14,488,077
Interest Rate Swaps
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2018	12,370,000
Additions	26,950,000
Settlement, Termination, Expiration or Exercise	(25,320,000)
Notional Amount as of December 31, 2019	14,000,000
Future Contracts
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2018	1,689,900
Additions	3,625,800
Settlement, Termination, Expiration or Exercise	(5,315,700)
Notional Amount as of December 31, 2019	0
Currency Forward Contracts
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2018	23,149
Additions	101,597
Settlement, Termination, Expiration or Exercise	(101,635)
Notional Amount as of December 31, 2019	23,111
Credit Derivatives
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2018	526,912
Additions	0
Settlement, Termination, Expiration or Exercise	(61,946)
Notional Amount as of December 31, 2019	$ 464,966