Claim, Claim Adjustment Expense and Future Policy Benefit Reserves - Schedule of Impact of Loss Portfolio Transfer on the Consolidated Statement of Operations (Detail) - CNA Financial Corporation [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Additional amounts ceded under LPT:
Net A&EP adverse development before consideration of LPT	$ 150	$ 178	$ 60
Provision for uncollectible third-party reinsurance on A&EP	(25)	(16)
Total additional amounts ceded under LPT	125	162	60
Retroactive reinsurance benefit recognized	(107)	(114)	(68)
Pretax impact of deferred retroactive reinsurance	$ 18	$ 48	$ (8)