Reinsurance - Earned Consolidated Property Casualty Insurance Premiums on Assumed and Ceded Business (Detail) - Consolidated Property and Casualty Insurance Entity - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct earned premiums	$ 1,153	$ 1,110	$ 3,409	$ 3,279
Assumed earned premiums	22	3	53	8
Ceded earned premiums	(42)	(37)	(119)	(111)
Earned premiums	$ 1,133	$ 1,076	$ 3,343	$ 3,176