Reinsurance - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) Reinsurer	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Effects of Reinsurance [Line Items]
Reinsurance recoverables included in other long-term assets	$ 668	$ 646
Percentage of reinsurance recoverables resulting from 100% coinsurance agreements	43.00%	45.00%
Premiums ceded	$ 821	$ 357	$ 33
Benefits ceded	$ 666	$ 272	$ 70
Number of reinsurers comprising other reinsurance recoverables balance | Reinsurer	18
Maximum carrying value of reinsurance recoverables for a number of reinsurers	$ 85
Number of reinsurers who have placed cash and securities in trusts | Reinsurer	3
Cash and securities in trusts held by certain reinsurers	$ 104
100% Coinsurance Agreements
Effects of Reinsurance [Line Items]
Percentage of coinsurance agreement	100.00%