(Favorable) Unfavorable Prior Accident Year Loss Reserve Development (Parenthetical) (Detail)	Mar. 20, 2017	Mar. 19, 2017
Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims [Abstract]
Ogden discount rate	(0.75%)	2.50%

Discount rate issued by the U.K. Ministry of Justice used to calculate lump-sum bodily injury payouts in personal injury insurance claims in the U.K.

No definition available.