Reinsurance - Earned Life Insurance Premiums on Ceded Business (Detail) - Life Insurance Segment - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct earned premiums	$ 72	$ 74	$ 223	$ 220
Ceded earned premiums	(16)	(16)	(50)	(45)
Earned premiums	$ 56	$ 58	$ 173	$ 175