Schedule of Pre-Tax Income (Loss) Effects of Cash Flow Hedges (Detail) - Cash Flow Hedges - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) recognized in OCI	$ (106)	$ (391)	$ 39	$ (643)
Gain (loss) reclassified into net income from OCI	58	56	119	113
Gain (loss) recognized in net income (loss)	0	0	0	0
Interest Rate Swaps Hedging Assets \| Net Investment Income
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) recognized in OCI	(104)	(405)	42	(655)
Gain (loss) reclassified into net income from OCI	55	57	109	112
Interest Rate Swaps Hedging Assets \| Gain (Loss) on Investments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) recognized in OCI	0		0	0
Gain (loss) reclassified into net income from OCI	3		8	2
Gain (loss) recognized in net income (loss)	0	0	0	0
Interest Rate Swaps Hedging Liabilities \| Interest Expense
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) recognized in OCI			0	0
Gain (loss) reclassified into net income from OCI			(1)	(2)
Interest Rate Swaps Hedging Liabilities \| Gain (Loss) on Investments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) recognized in OCI		0	0
Gain (loss) reclassified into net income from OCI		(1)	1
Gain (loss) recognized in net income (loss)		0	0	0
Foreign currency swaps \| Net Investment Income
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) recognized in OCI	(2)	14	(3)	12
Gain (loss) reclassified into net income from OCI	0	0	0	1
Foreign currency swaps \| Gain (Loss) on Investments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) recognized in OCI			0
Gain (loss) reclassified into net income from OCI			2
Gain (loss) recognized in net income (loss)	$ 0	$ 0	$ 0	$ 0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

+ Details

Name:	us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4C

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1),(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480238/815-25-50-1

+ Details

Name:	us-gaap_DerivativeInstrumentsGainLossRecognizedInIncomeIneffectivePortionAndAmountExcludedFromEffectivenessTestingNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, before tax and reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-11

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4C
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4C

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480627/815-20-45-3

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4A

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 10A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-10A

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, before tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

+ Details

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

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=gnw_InterestRateSwapsHedgingAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=gnw_NetInvestmentIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_GainLossOnInvestmentsMember1
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=gnw_InterestRateSwapsHedgingLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_InterestExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CurrencySwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: