Statutory Accounting Practices - Combined Statutory Capital and Surplus and Net Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus	$ 88	$ 63
Combined Continental Casualty Companies [Member]
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus	10,411	10,726
Statutory Net Income	$ 1,405	$ 1,029	$ 1,033