Statutory Accounting Practices - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Statutory Accounting Practices [Line Items]
Increase in statutory capital and surplus	$ 90
Combined Continental Casualty Companies [Member]
Statutory Accounting Practices [Line Items]
Increase in statutory capital and surplus	10,723	$ 11,155
Dividends payable without prior supervisory approval	1,100
Dividends paid	$ 900
Statutory capital and surplus percentage	266.00%	270.00%