Deferred Acquisition Costs - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Sep. 30, 2012	Mar. 31, 2012
Deferred Policy Acquisition Costs [Line Items]
DAC amortization expense related to life block transaction		$ 142
DAC Amortization expense related to recoverability testing	$ 39

Amortization of deferred acquisition costs associated with certain term life insurance policies under a new reinsurance treaty as part of a life block transaction.

No definition available.

Name:	gnw_DeferredPolicyAcquisitionCostAmortizationExpenseRelatedToLifeBlockTransaction
Namespace Prefix:	gnw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration