Summary of Net Operating Income (Loss) for Segments and Corporate and Other Activities (Parenthetical) (Detail) - Net Investment (Gains) Losses - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Adjustment for DAC and other intangibles and certain benefit reserves	$ (3)	$ 0	$ (7)	$ 0
Adjustment for portion attributable to noncontrolling interests	$ 13	$ 23	$ 1	$ 59

Adjustment to net investment gains (losses) for DAC and other intangibles amortization and certain benefit reserves, before taxes, to arrive at net operating income (loss).

No definition available.

Name:	gnw_AdjustmentForDeferredAcquisitionCostsAndOtherIntangibleAmortizationAndCertainBenefitReserves
Namespace Prefix:	gnw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration