Reserves in Addition to Account Balance, Based on Expected No-Lapse Guarantee Benefits and Expected Policy Assessments (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Liability for Future Policy Benefit, by Product Segment [Line Items]
Life policy and investment contract reserves	$ 2,641	$ 2,583
Life policy reserves:
Liability for Future Policy Benefit, by Product Segment [Line Items]
Life policy and investment contract reserves	1,036	987
Life policy reserves: | Ordinary/traditional life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Life policy and investment contract reserves	991	943
Life policy reserves: | Other
Liability for Future Policy Benefit, by Product Segment [Line Items]
Life policy and investment contract reserves	45	44
Investment contract reserves:
Liability for Future Policy Benefit, by Product Segment [Line Items]
Life policy and investment contract reserves	1,605	1,596
Investment contract reserves: | Deferred annuities
Liability for Future Policy Benefit, by Product Segment [Line Items]
Life policy and investment contract reserves	864	860
Investment contract reserves: | Universal life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Life policy and investment contract reserves	565	558
Investment contract reserves: | Structured settlements
Liability for Future Policy Benefit, by Product Segment [Line Items]
Life policy and investment contract reserves	170	174
Investment contract reserves: | Other
Liability for Future Policy Benefit, by Product Segment [Line Items]
Life policy and investment contract reserves	$ 6	$ 4