Reserves in Addition to Account Balance, Based on Expected No-Lapse Guarantee Benefits and Expected Policy Assessments (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	$ 2,861	$ 2,835
Life policy reserves:
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,295	1,276
Life policy reserves: | Ordinary/traditional life
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,245	1,226
Life policy reserves: | Other
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	50	50
Investment contract reserves:
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,566	1,559
Investment contract reserves: | Deferred annuities
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	754	760
Investment contract reserves: | Universal life
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	653	640
Investment contract reserves: | Structured Settlement Annuity
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	151	151
Investment contract reserves: | Other
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	$ 8	$ 8