Reserves in Addition to Account Balance, Based on Expected No-Lapse Guarantee Benefits and Expected Policy Assessments (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	$ 2,900	$ 2,835
Life policy reserves:
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,338	1,276
Life policy reserves: | Ordinary/traditional life
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,287	1,226
Life policy reserves: | Other
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	51	50
Investment contract reserves:
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,562	1,559
Investment contract reserves: | Deferred annuities
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	760	760
Investment contract reserves: | Universal life
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	646	640
Investment contract reserves: | Structured Settlement Annuity
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	147	151
Investment contract reserves: | Other
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	$ 9	$ 8