Reserves in Addition to Account Balance, Based on Expected No-Lapse Guarantee Benefits and Expected Policy Assessments (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	$ 2,999	$ 2,915
Life policy reserves:
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,410	1,353
Life policy reserves: | Ordinary/traditional life
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,358	1,301
Life policy reserves: | Other
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	52	52
Investment contract reserves:
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,589	1,562
Investment contract reserves: | Deferred annuities
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	767	761
Investment contract reserves: | Universal life
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	674	647
Investment contract reserves: | Structured Settlement Annuity
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	139	145
Investment contract reserves: | Other
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	$ 9	$ 9