Claim and Claim Adjustment Expense Reserves - Schedule of Impact of Loss Portfolio Transfer on the Consolidated Statement of Operations (Detail) - CNA Financial [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Claim And Claim Adjustment Expense Reserves [Line Items]
Net A&EP adverse development before consideration of LPT	$ 200	$ 150
Retroactive reinsurance benefit recognized	(107)	(85)	$ (13)
Pretax impact of A&EP reserve development and the LPT	$ 93	$ 65	$ (13)