Investments - Components of OTTI Losses Recognized in Earnings by Asset Type (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net OTTI losses recognized in earnings	$ 2	$ 6	$ 4
Corporate Bonds and Other [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net OTTI losses recognized in earnings	$ 2	5	$ 4
Total Asset-Backed [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net OTTI losses recognized in earnings		$ 1