Reserves in Addition to Account Balance, Based on Expected No-Lapse Guarantee Benefits and Expected Policy Assessments (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	$ 2,816	$ 2,779
Life policy reserves:
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,255	1,197
Life policy reserves: | Ordinary/traditional life
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,206	1,149
Life policy reserves: | Other
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	49	48
Investment contract reserves:
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,561	1,582
Investment contract reserves: | Deferred annuities
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	768	787
Investment contract reserves: | Universal life
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	635	632
Investment contract reserves: | Structured Settlement Annuity
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	152	156
Investment contract reserves: | Other
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	$ 6	$ 7