Account Balances of Variable Annuity Contract with Death or Living Benefit Guarantees Invested in Separate Account Investment Options (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account investment	$ 5,352	$ 6,290
Balanced funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account investment	3,304	3,848
Equity funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account investment	1,387	1,639
Bond funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account investment	576	707
Money market funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account investment	$ 85	$ 96