Derivatives and Hedging Activities - Outstanding Interest Rate Swaptions and Derivative Instrument Information (Detail)	6 Months Ended
	Jun. 30, 2017 USD ($)
Derivative Interest Rate Swaptions
Notional Amount as of January 1, 2017	$ 7,132,274,000
Additions	1,537,860,000
Settlement, Termination, Expiration or Exercise	(137,304,000)
Notional Amount as of June 30, 2017	8,532,830,000
Interest Rate Swaps
Derivative Interest Rate Swaptions
Notional Amount as of January 1, 2017	6,500,000,000
Additions	1,400,000,000
Settlement, Termination, Expiration or Exercise	0
Notional Amount as of June 30, 2017	7,900,000,000
Currency Forward Contracts
Derivative Interest Rate Swaptions
Notional Amount as of January 1, 2017	62,308,000
Additions	137,860,000
Settlement, Termination, Expiration or Exercise	(131,575,000)
Notional Amount as of June 30, 2017	68,593,000
Credit Derivatives
Derivative Interest Rate Swaptions
Notional Amount as of January 1, 2017	569,966,000
Additions	0
Settlement, Termination, Expiration or Exercise	(5,729,000)
Notional Amount as of June 30, 2017	$ 564,237,000