Information about Variable Annuity Products with Death and Living Benefit Guarantees (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Guaranteed minimum standard death benefit
Net Amount at Risk by Product and Guarantee [Line Items]
Death benefits account value	$ 2,365	$ 2,364
Net amount at risk	$ 2	$ 4
Average attained age of contractholders	74 years	73 years
Guaranteed minimum enhanced death benefit
Net Amount at Risk by Product and Guarantee [Line Items]
Death benefits account value	$ 2,489	$ 2,611
Net amount at risk	$ 114	$ 157
Average attained age of contractholders	74 years	74 years
Guaranteed minimum living benefit
Net Amount at Risk by Product and Guarantee [Line Items]
Death benefits account value	$ 2,671	$ 2,781
Guaranteed annuitization benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Death benefits account value	$ 1,198	$ 1,177