Statutory Accounting Practices - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Statutory Accounting Practices [Line Items]
Increase in statutory capital and surplus	$ 67	$ 90
Combined Continental Casualty Companies [Member]
Statutory Accounting Practices [Line Items]
Increase in statutory capital and surplus	10,748	$ 10,723
Dividends payable without prior supervisory approval	1,100
Dividends paid	$ 765
Statutory capital and surplus percentage	270.00%	266.00%