Summary of Significant Observable Inputs Used for Fair Value Measurements for Living Benefits Liabilities Classified as Level 3 (Detail) - Living Benefits [Member]	12 Months Ended
	Dec. 31, 2018
Summary of significant unobservable inputs used for fair value measurements for living benefits liabilities
Fair value unobservable inputs Discount rate		[1]
Minimum [Member]
Summary of significant unobservable inputs used for fair value measurements for living benefits liabilities
Fair value unobservable inputs Mortality	0.10%	[2]
Fair value unobservable inputs Lapse	0.00%	[3]
Fair value unobservable inputs wait period	0 years	[4]
Fair value unobservable inputs efficiency of benefit utilization	60.00%	[5],[6]
Fair value unobservable inputs index Volatility	15.00%
Maximum [Member]
Summary of significant unobservable inputs used for fair value measurements for living benefits liabilities
Fair value unobservable inputs Mortality	10.00%	[2]
Fair value unobservable inputs Lapse	35.00%	[3]
Fair value unobservable inputs wait period	30 years	[4]
Fair value unobservable inputs efficiency of benefit utilization	100.00%	[5],[6]
Fair value unobservable inputs index Volatility	25.00%

[1] Incorporates the liquidity and non-performance risk adjustment. The liquidity spread takes into consideration market observables for spreads in illiquid assets. The non-performance risk adjustment reflects an additional spread over LIBOR, determined by market observables for similarly rated public bonds.

[2] Represents the mortality for the majority of business with living benefits, with policyholder issue ages ranging from 45 to 85.

[3] Certain scenarios could drive dynamic lapses outside of the specified range. The range shown represents lapses for the vast majority of scenarios.

[4] A portion of the contractholders could never use the benefit, which would extend the range to an indeterminate period.

[5] A portion of the contractholders could withdraw more than the benefit guarantee allows. For these policies, the excess withdrawals are assumed to be temporary before reverting back to 100% utilization.

[6] The unobservable input is not applicable to GMABs.