Deferred Policy Acquisition Costs - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Policy Acquisition Costs Disclosures [Abstract]
Amortization of DAC related to unlocks	$ (17)	$ (69)	$ 21
Other decrease in amortization	$ (43)	$ (13)	$ (75)

Amount of amortization expense (reversal of amortization expense) of deferred policy acquisition costs from a revision in estimated gross profit or estimated gross margin.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=35755530&loc=d3e11264-158415

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 30
-Section 35
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=95462302&loc=d3e10129-158409

Name:	us-gaap_DeferredPolicyAcquisitionCostAmortizationExpenseEffectOfAdjustmentsToEstimatedGrossProfitOrEstimatedGrossMargin
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration