Fair Value Measurements (Narrative) (Detail) $ in Millions		12 Months Ended
		Dec. 31, 2018 USD ($) Year	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed Living Benefits Lapse Rate Base Lower Range		3.00%
Guaranteed Living Benefits Lapse Rate Base Upper Range		9.00%
Guaranteed Living Benefits Lapse Rate Spike Lower Range		9.00%
GLB - spike lapse rate - upper range		33.00%
GLB - Ultimate lapse rate		10.00%
GLB - Length of ultimate lapse rate period, years | Year		2
Guaranteed Living Benefits Adjustment Factor For Valuable Guarantees Lower Range		15.00%
Guaranteed Living Benefits Adjustment Factor For Valuable Guarantees Upper Range		75.00%
Derivative, Gain (Loss) on Derivative, Net		$ (330)	$ 87	$ (126)
Guaranteed Minimum Income Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, Gain (Loss) on Derivative, Net	[1]	(248)	$ 364	$ 53
Guaranteed Minimum Income Benefit | Variable Annuity [Member] | Measurement Input, Lapse Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, Gain (Loss) on Derivative, Net		20
Guaranteed Minimum Income Benefit | Variable Annuity [Member] | Measurement Input, Withdrawal Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, Gain (Loss) on Derivative, Net		11
Guaranteed Minimum Income Benefit | Variable Annuity [Member] | Measurement Input, Mortality Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, Gain (Loss) on Derivative, Net		$ 28
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notice period for redemption for alternative investments investment funds, days		5 days
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notice period for redemption for alternative investments investment funds, days		120 days

[1] Excludes foreign exchange gains (losses) related to GLB.