Summary of Segments and Corporate and Other Activities (Detail) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Premiums																	$ 4,519	$ 4,004	$ 4,160
Net investment income																	3,262	3,200	3,159
Net investment gains (losses)																	(146)	265	72
Policy fees and other income																	795	826	978
Total revenues	$ 2,013	[1]	$ 2,143	[1]	$ 2,159	[1]	$ 2,115	[1]	$ 1,686	[2]	$ 2,215	[2]	$ 2,223	[2]	$ 2,171	[2]	8,430	8,295	8,369
Benefits and other changes in policy reserves																	5,684	5,179	5,245
Interest credited																	611	646	696
Acquisition and operating expenses, net of deferrals																	997	1,022	1,273
Amortization of deferred acquisition costs and intangibles																	391	435	498
Interest expense																	299	284	337
Total benefits and expenses	2,426	[3]	1,870	[3]	1,799	[3]	1,887	[3]	1,976	[4]	1,929	[4]	1,822	[4]	1,839	[4]	7,982	7,566	8,049
Income (loss) from continuing operations before income taxes																	448	729	320
Provision (benefit) for income taxes									456								151	(207)	358
Income (loss) from continuing operations	(327)	[5]	210	[5]	249	[5]	165	[5]	265	[6]	184	[6]	271	[6]	216	[6]	297	936	(38)
Loss from discontinued operations, net of taxes	0		0		0		0				(9)						0	(9)	(29)
Net income (loss)	(327)	[5]	210	[5]	249	[5]	165	[5]	265	[6]	175	[6]	271	[6]	216	[6]	297	927	(67)
Less: net income (loss) attributable to noncontrolling interests																	178	110	210
Net income (loss) available to Genworth Financial, Inc.'s common stockholders	(329)	[5]	$ 146	[5]	$ 190	[5]	$ 112	[5]	353	[6]	$ 107	[6]	$ 202	[6]	$ 155	[6]	119	817	(277)
Total assets	100,923								105,297								100,923	105,297
U.S. Mortgage Insurance | Segment, Continuing Operations
Segment Reporting Information [Line Items]
Premiums																	746	695	660
Net investment income																	93	73	63
Net investment gains (losses)																	0	0	(1)
Policy fees and other income																	2	4	4
Total revenues																	841	772	726
Benefits and other changes in policy reserves																	36	107	160
Interest credited																	0	0	0
Acquisition and operating expenses, net of deferrals																	169	165	167
Amortization of deferred acquisition costs and intangibles																	14	14	12
Interest expense																	0	0	0
Total benefits and expenses																	219	286	339
Income (loss) from continuing operations before income taxes																	622	486	387
Provision (benefit) for income taxes																	132	175	138
Income (loss) from continuing operations																	490	311	249
Loss from discontinued operations, net of taxes																	0	0	0
Net income (loss)																	490	311	249
Less: net income (loss) attributable to noncontrolling interests																	0	0	0
Net income (loss) available to Genworth Financial, Inc.'s common stockholders																	490	311	249
Total assets	3,583								3,273								3,583	3,273
Canada Mortgage Insurance
Segment Reporting Information [Line Items]
Net investment gains (losses)	(107)
Total revenues	114
Canada Mortgage Insurance | Segment, Continuing Operations
Segment Reporting Information [Line Items]
Premiums																	525	519	481
Net investment income																	138	132	126
Net investment gains (losses)																	(137)	128	37
Policy fees and other income																	0	1	1
Total revenues																	526	780	645
Benefits and other changes in policy reserves																	78	54	104
Interest credited																	0	0	0
Acquisition and operating expenses, net of deferrals																	70	80	77
Amortization of deferred acquisition costs and intangibles																	43	43	39
Interest expense																	18	18	18
Total benefits and expenses																	209	195	238
Income (loss) from continuing operations before income taxes																	317	585	407
Provision (benefit) for income taxes																	84	191	113
Income (loss) from continuing operations																	233	394	294
Loss from discontinued operations, net of taxes																	0	0	0
Net income (loss)																	233	394	294
Less: net income (loss) attributable to noncontrolling interests																	108	190	135
Net income (loss) available to Genworth Financial, Inc.'s common stockholders																	125	204	159
Total assets	5,038								5,534								5,038	5,534
Australia Mortgage Insurance | Segment, Continuing Operations
Segment Reporting Information [Line Items]
Premiums																	373	(140)	337
Net investment income																	67	75	94
Net investment gains (losses)																	(15)	25	9
Policy fees and other income																	2	0	0
Total revenues																	427	(40)	440
Benefits and other changes in policy reserves																	110	109	113
Interest credited																	0	0	0
Acquisition and operating expenses, net of deferrals																	65	67	96
Amortization of deferred acquisition costs and intangibles																	43	24	14
Interest expense																	9	9	10
Total benefits and expenses																	227	209	233
Income (loss) from continuing operations before income taxes																	200	(249)	207
Provision (benefit) for income taxes																	60	(90)	67
Income (loss) from continuing operations																	140	(159)	140
Loss from discontinued operations, net of taxes																	0	0	0
Net income (loss)																	140	(159)	140
Less: net income (loss) attributable to noncontrolling interests																	70	(80)	75
Net income (loss) available to Genworth Financial, Inc.'s common stockholders																	70	(79)	65
Total assets	2,534								2,973								2,534	2,973
U.S. Life Insurance | Segment, Continuing Operations
Segment Reporting Information [Line Items]
Premiums																	2,867	2,922	2,670
Net investment income																	2,781	2,755	2,726
Net investment gains (losses)																	29	134	128
Policy fees and other income																	641	660	726
Total revenues																	6,318	6,471	6,250
Benefits and other changes in policy reserves																	5,416	4,880	4,822
Interest credited																	461	506	565
Acquisition and operating expenses, net of deferrals																	584	572	648
Amortization of deferred acquisition costs and intangibles																	257	328	403
Interest expense																	16	13	38
Total benefits and expenses																	6,734	6,299	6,476
Income (loss) from continuing operations before income taxes																	(416)	172	(226)
Provision (benefit) for income taxes																	(68)	60	(80)
Income (loss) from continuing operations																	(348)	112	(146)
Loss from discontinued operations, net of taxes																	0	0	0
Net income (loss)																	(348)	112	(146)
Less: net income (loss) attributable to noncontrolling interests																	0	0	0
Net income (loss) available to Genworth Financial, Inc.'s common stockholders																	(348)	112	(146)
Total assets	79,799								81,295								79,799	81,295
Runoff | Segment, Continuing Operations
Segment Reporting Information [Line Items]
Premiums																	0	0	0
Net investment income																	174	160	147
Net investment gains (losses)																	(33)	16	(14)
Policy fees and other income																	153	163	169
Total revenues																	294	339	302
Benefits and other changes in policy reserves																	39	26	42
Interest credited																	150	140	131
Acquisition and operating expenses, net of deferrals																	57	61	68
Amortization of deferred acquisition costs and intangibles																	33	24	29
Interest expense																	0	2	1
Total benefits and expenses																	279	253	271
Income (loss) from continuing operations before income taxes																	15	86	31
Provision (benefit) for income taxes																	2	25	6
Income (loss) from continuing operations																	13	61	25
Loss from discontinued operations, net of taxes																	0	0	0
Net income (loss)																	13	61	25
Less: net income (loss) attributable to noncontrolling interests																	0	0	0
Net income (loss) available to Genworth Financial, Inc.'s common stockholders																	13	61	25
Total assets	9,963								10,907								9,963	10,907
Corporate and Other
Segment Reporting Information [Line Items]
Provision (benefit) for income taxes									11
Corporate and Other | Segment, Continuing Operations
Segment Reporting Information [Line Items]
Premiums																	8	8	12
Net investment income																	9	5	3
Net investment gains (losses)																	10	(38)	(87)
Policy fees and other income																	(3)	(2)	78
Total revenues																	24	(27)	6
Benefits and other changes in policy reserves																	5	3	4
Interest credited																	0	0	0
Acquisition and operating expenses, net of deferrals																	52	77	217
Amortization of deferred acquisition costs and intangibles																	1	2	1
Interest expense																	256	242	270
Total benefits and expenses																	314	324	492
Income (loss) from continuing operations before income taxes																	(290)	(351)	(486)
Provision (benefit) for income taxes																	(59)	(568)	114
Income (loss) from continuing operations																	(231)	217	(600)
Loss from discontinued operations, net of taxes																	0	(9)	(29)
Net income (loss)																	(231)	208	(629)
Less: net income (loss) attributable to noncontrolling interests																	0	0	0
Net income (loss) available to Genworth Financial, Inc.'s common stockholders																	(231)	208	$ (629)
Total assets	$ 6								$ 1,315								$ 6	$ 1,315

[1] Includes net investment losses of $114 million in the fourth quarter of 2018 primarily from our Canada Mortgage Insurance segment. These losses were primarily related to derivative losses on foreign currency swaps and forwards, and losses on preferred equity securities primarily driven by a decrease in interest rates in Canada during the fourth quarter of 2018.

[2] Our Australian mortgage insurance business completed a review of its premium earnings pattern in the fourth quarter of 2017 and recorded $468 million of lower earned premiums. The review indicated an observed and expected continuation of a longer duration between policy inception and first loss event.

[3] Our long-term care insurance business completed its annual review of claim reserves in the fourth quarter of 2018, which resulted in higher total benefits and expenses of $291 million driven mostly by updates to several assumptions and methodologies, including benefit utilization rates, claim termination rates and other assumptions. Also in our long-term care insurance business, we refined our estimate of unreported policy terminations, which resulted in an unfavorable reserve adjustment of $36 million in 2018. Our life insurance business completed its annual review of assumptions in the fourth quarter of 2018, which resulted in higher total benefits and expenses of $108 million in our universal and term universal life insurance products driven mostly by lower expected growth in interest rates and emerging mortality experience primarily in our term universal life insurance product.

[4] Our life insurance business completed its annual review of assumptions in the fourth quarter of 2017, which resulted in higher total benefits and expenses of $117 million in our universal and term universal life insurance products driven mostly by emerging mortality experience and from prolonged low interest rates. In addition, we recorded lower total benefits and expenses of $18 million in our Australian mortgage insurance business associated with changes to their premium earnings pattern, as described above.

[5] In the fourth quarter of 2018, our long-term care insurance business recorded a $230 million unfavorable adjustment, net of taxes, related to its annual review of claim reserves, as described above. In addition, our long-term care insurance business recorded a $28 million unfavorable reserve adjustment, net of taxes, related to a refined estimate of unreported policy terminations. Our life insurance business recorded an unfavorable adjustment, net of taxes, of $91 million resulting from its annual review of assumptions, as described above. Our Canada mortgage insurance business recorded net investment losses, net of taxes, of $107 million, as described above.

[6] In the fourth quarter of 2017, we recorded $456 million of net tax benefits primarily from changes in U.S. tax legislation under the TCJA and other items. These tax benefits were mostly related to a $258 million release of a valuation allowance recorded in 2016, the impact from changes in the federal tax rate and the release of shareholder liability taxes, partially offset by higher transition taxes. Our valuation allowance was reduced by $258 million principally related to the TCJA and from improvements in business performance, mostly in our U.S. mortgage insurance business, as well as lower operating earnings volatility in our U.S. life insurance businesses. Our Australian mortgage insurance business completed a review of the premium earnings pattern, as described above, which resulted in an unfavorable adjustment of $152 million, net of taxes and noncontrolling interests. A portion of this loss, $11 million, was recorded in Corporate and Other activities in connection with our allocation methodology for income taxes. We also completed our annual review of assumptions in our life insurance business in the fourth quarter of 2017, as described above, which resulted in a $74 million unfavorable adjustment, net of taxes, in our universal and term universal life insurance products.