Investments - Additional Information (Detail)		12 Months Ended
	Dec. 31, 2016 USD ($) Investment	Dec. 31, 2016 USD ($) Investment	Dec. 31, 2015 USD ($) Investment	Dec. 31, 2014
Schedule of Investments [Line Items]
Value of non-income producing fixed maturity securities held	$ 0	$ 0	$ 54,000,000
Number of Investments not exceeds 10% of shareholders equity | Investment	0	0	0
Additional other than temporary impairment losses	$ 0
Carrying value of limited partnerships	$ 3,200,000,000	$ 3,200,000,000	$ 3,300,000,000
Undistributed earnings of limited partnerships		$ 820,000,000	$ 952,000,000
Percentage of carrying value reported on a current basis		70.40%
Percentage of carrying value reported on one month lag		13.40%
Percentage of limited partnerships comprising of the carrying value that employ hedge fund strategies	76.60%	76.60%	76.60%
Percentage of limited partnerships comprising of the carrying value that invested in private debt and equity	19.80%	19.80%	23.40%
Percentage of limited partnerships employing hedge fund strategies focused on equity investments	59.80%	59.80%
Percentage of limited partnerships employing hedge fund strategies with a multi-strategy approach	25.50%	25.50%
Percentage of limited partnerships employing hedge fund strategies focused on distressed investments	11.10%	11.10%
Percentage of limited partnerships employing hedge fund strategies focused on fixed income investments	3.60%	3.60%
Ownership percentage of aggregate partnership equity	3.50%	3.50%	2.80%
Changes in ownership percentage of aggregate partnership equity		4.00%	2.80%	4.30%
Withdrawal provisions limited partnership investments, description		The Company's limited partnership investments contain withdrawal provisions that generally limit liquidity for a period of thirty days up to one year and in some cases do not permit withdrawals until the termination of the partnership. Typically, withdrawals require advance written notice of up to 90 days.
Future capital call commitments	$ 380,000,000	$ 380,000,000
Commitments to purchase various privately placed debt securities, including bank loans	130,000,000	130,000,000
Commitments to sell various privately placed debt securities, including bank loans	121,000,000	121,000,000
Securities deposited	2,300,000,000	2,300,000,000	$ 2,800,000,000
Cash and securities with carrying values deposited as collateral for letters of credit	514,000,000	514,000,000	364,000,000
Securities deposited as collateral for letters of credit	261,000,000	261,000,000	263,000,000
Ten Largest Limited Partnership Holdings [Member]
Schedule of Investments [Line Items]
Carrying value of limited partnerships	$ 1,500,000,000	$ 1,500,000,000	$ 1,500,000,000