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, 2018	Dec. 31, 2017	Dec. 31, 2016
Additional amounts ceded under LPT:
Net A&EP adverse development before consideration of LPT	$ 178	$ 60	$ 200
Provision for uncollectible third-party reinsurance on A&EP	(16)
Total additional amounts ceded under LPT	162	60	200
Retroactive reinsurance benefit recognized	(114)	(68)	(107)
Pretax impact of deferred retroactive reinsurance	$ 48	$ (8)	$ 93