Claim and Claim Adjustment Expense Reserves - Net Prior Year Development (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development	$ (7)	$ 25
Pretax (favorable) unfavorable premium development	9	(31)
Total pretax (favorable) unfavorable net prior year development	2	(6)
Specialty [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development	2	(3)
Pretax (favorable) unfavorable premium development	(6)	(6)
Total pretax (favorable) unfavorable net prior year development	(4)	(9)
Commercial [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development	(5)	18
Pretax (favorable) unfavorable premium development	(1)	(18)
Total pretax (favorable) unfavorable net prior year development	(6)
International [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development	(4)	10
Pretax (favorable) unfavorable premium development	16	(7)
Total pretax (favorable) unfavorable net prior year development	$ 12	$ 3