Accounting Changes - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Disclosure of Accounting Changes [Line Items]
Retained earnings	$ 1,317	$ 1,461
Commercial mortgage loans
Disclosure of Accounting Changes [Line Items]
Accrued interest carrying value in Accrued investment income	24
Fixed maturity securities
Disclosure of Accounting Changes [Line Items]
Accrued interest carrying value in Accrued investment income	565
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment | Investments carried at amortized cost
Disclosure of Accounting Changes [Line Items]
Adoption of new accounting guidance, deferred tax impact	6
Retained earnings	23
Accounting Standards Update 2016-13 | Off-balance sheet credit exposures | Cumulative Effect, Period of Adoption, Adjustment
Disclosure of Accounting Changes [Line Items]
Retained earnings	1
Accounting Standards Update 2016-13 | Reinsurance recoverables | Cumulative Effect, Period of Adoption, Adjustment
Disclosure of Accounting Changes [Line Items]
Adoption of new accounting guidance, deferred tax impact	9
Retained earnings	$ 31