Remaining Contractual Maturity of Agreements (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	$ 75	$ 229
Securities lending	534	347
Total repurchase agreements and securities lending	609	576
U.S. government, agencies and government-sponsored enterprises
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	75	229
Equity Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	7	5
Fixed maturity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	527	342
Fixed maturity securities | U.S. government, agencies and government-sponsored enterprises
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	224	18
Fixed maturity securities | Non-U.S. government
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	34	39
Fixed maturity securities | U.S. corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	159	95
Fixed maturity securities | Non-U.S. corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	110	190
Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	534	347
Total repurchase agreements and securities lending	534	347
Overnight and continuous | U.S. government, agencies and government-sponsored enterprises
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	0	0
Overnight and continuous | Equity Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	7	5
Overnight and continuous | Fixed maturity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	527	342
Overnight and continuous | Fixed maturity securities | U.S. government, agencies and government-sponsored enterprises
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	224	18
Overnight and continuous | Fixed maturity securities | Non-U.S. government
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	34	39
Overnight and continuous | Fixed maturity securities | U.S. corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	159	95
Overnight and continuous | Fixed maturity securities | Non-U.S. corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	110	190
Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Total repurchase agreements and securities lending	0	58
Up to 30 days | U.S. government, agencies and government-sponsored enterprises
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	0	58
Up to 30 days | Equity Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Up to 30 days | Fixed maturity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Up to 30 days | Fixed maturity securities | U.S. government, agencies and government-sponsored enterprises
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Up to 30 days | Fixed maturity securities | Non-U.S. government
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Up to 30 days | Fixed maturity securities | U.S. corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Up to 30 days | Fixed maturity securities | Non-U.S. corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
31 - 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Total repurchase agreements and securities lending	16	25
31 - 90 days | U.S. government, agencies and government-sponsored enterprises
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	16	25
31 - 90 days | Equity Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
31 - 90 days | Fixed maturity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
31 - 90 days | Fixed maturity securities | U.S. government, agencies and government-sponsored enterprises
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
31 - 90 days | Fixed maturity securities | Non-U.S. government
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
31 - 90 days | Fixed maturity securities | U.S. corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
31 - 90 days | Fixed maturity securities | Non-U.S. corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Total repurchase agreements and securities lending	59	146
Greater than 90 days | U.S. government, agencies and government-sponsored enterprises
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	59	146
Greater than 90 days | Equity Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Greater than 90 days | Fixed maturity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Greater than 90 days | Fixed maturity securities | U.S. government, agencies and government-sponsored enterprises
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Greater than 90 days | Fixed maturity securities | Non-U.S. government
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Greater than 90 days | Fixed maturity securities | U.S. corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	0	0
Greater than 90 days | Fixed maturity securities | Non-U.S. corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending	$ 0	$ 0