Reinsurance - Incurred Consolidated Property Casualty Insurance Loss and Loss Expenses on Assumed and Ceded Business (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Incurred loss and loss expenses	$ 821	$ 712	$ 1,545	$ 1,461
Consolidated Property and Casualty Insurance Entity
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct incurred loss and loss expenses	792	675	1,440	1,366
Assumed incurred loss and loss expenses	11	1	21	0
Ceded incurred loss and loss expenses	(44)	(22)	(41)	(23)
Incurred loss and loss expenses	$ 759	$ 654	$ 1,420	$ 1,343