Net Unrealized Gains and Losses on Available-for-Sale Investment Securities Reflected as Separate Component of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions		Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Components of Net Unrealized Investment Gains Losses Included in Accumulated Other Comprehensive Income Loss [Line Items]
Net unrealized gains (losses) on fixed maturity securities without an allowance for credit losses	[1]	$ 9,218		$ 6,676
Net unrealized gains (losses) on fixed maturity securities with an allowance for credit losses	[1]	(12)		0
Adjustments to deferred acquisition costs, present value of future profits, sales inducements and benefit reserves		(6,998)		(4,789)
Income taxes, net		(473)		(406)
Net unrealized investment gains (losses)		1,735		1,481
Less: net unrealized investment gains (losses) attributable to noncontrolling interests		24		25
Net unrealized investment gains (losses) attributable to Genworth Financial, Inc.		$ 1,711	$ 1,811	$ 1,456	$ 1,675	$ 1,305	$ 595

[1] Excludes foreign exchange.