Statutory Accounting Practices - Combined Statutory Capital and Surplus and Net Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus	$ 67	$ 90
Combined Continental Casualty Companies [Member]
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus	10,748	10,723
Statutory Net Income	$ 1,033	$ 1,148	$ 914