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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct earned premiums	$ 1,189	$ 1,137	$ 2,352	$ 2,256
Assumed earned premiums	33	16	60	31
Ceded earned premiums	(41)	(39)	(80)	(77)
Earned premiums	$ 1,181	$ 1,114	$ 2,332	$ 2,210