Summary of Reserve Balances for Variable Annuity Contracts with Guarantees (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Summarizes the reserve balances, for variable annuity contracts with guarantees
Reserve balances on guarantees	$ 1,100	$ 915
GMDB [Member]
Summarizes the reserve balances, for variable annuity contracts with guarantees
Reserve balances on guarantees	223	164
GLWB [Member]
Summarizes the reserve balances, for variable annuity contracts with guarantees
Reserve balances on guarantees	$ 554	$ 300

Sum of the amount of expected guaranteed benefits in excess of the projected account balances for minimum guaranteed benefit contracts, as of the balance sheet date, net of reinsurance recoverables, for all guaranteed benefit types.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=6588021&loc=d3e7104-158389

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 80
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473

Name:	us-gaap_GuaranteedBenefitLiabilityNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant