Claim and Claim Adjustment Expense Reserves - Impact of Loss Portfolio Transfer on Consolidated Condensed Statements of Income (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Insurance [Abstract]
Net A&EP adverse development before consideration of LPT		$ 200	$ 150	$ 200	$ 150
Provision for uncollectible third party reinsurance on A&EP	$ 0		0	0	0
Additional amounts ceded under LPT			150	200	150
Retroactive reinsurance benefit recognized	(9)		(66)	(82)	(71)
Pretax impact of unrecognized deferred retroactive reinsurance benefit	$ (9)		$ 84	$ 118	$ 79