Business, Basis of Presentation and Summary of Significant Accounting Policies - Restatement Adjustments (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Reserves for Group Annuity products										$ 510
Assumed variable annuity guarantee reserves										896
Restatement of Prior Year Income [Abstract]
Assumed variable annuity guarantee reserves										896
Reserves for Group Annuity products										510
Income (loss) from continuing operations before provision for income tax										3,536	$ 4,281	$ 5,651
Provision for income tax expense (benefit)										(1,470)	693	1,590
Income (loss) from continuing operations, net of income tax		$ 2,315	$ 883	$ 856	$ 952	$ (971)	$ 973	$ 1,686	$ 1,900	5,006	3,588	4,061
Income (loss) from discontinued operations, net of income tax		0	(968)	58	(76)	(1,370)	(435)	(1,361)	432	(986)	(2,734)	1,324
Net Income (Loss) Available to Common Stockholders, Basic		2,272	(97)	865	867	(2,388)	536	275	2,324	3,907	747	5,215
Balance Sheet Related Disclosures [Abstract]
Future policy benefits		177,974				166,636				177,974	166,636
Policyholder account balances		182,518				172,486				182,518	172,486	165,130
Other Policy-Related Balances		15,515				13,402				15,515	13,402
Deferred Tax Liabilities, Net		6,767				6,892				6,767	6,892
Other Liabilities		23,982				23,735				23,982	23,735
Liabilities		661,022				831,062				661,022	831,062
Retained Earnings (Accumulated Deficit)		26,527				34,683				26,527	34,683	35,672	$ 32,110
Accumulated Other Comprehensive Income (Loss), Net of Tax		7,427				5,366				7,427	5,366	4,767	10,714
Stockholders' Equity Attributable to Parent		58,676				67,531				58,676	67,531	68,098	72,208
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		58,870				67,702				58,870	67,702	68,568	72,715
Income Statement Related Disclosures [Abstract]
Insurance Commissions and Fees										5,510	5,483	5,570
Net Investment Income										17,363	16,790	16,205
Other net investment gains (losses)										(298)	424	668
Net investment gains (losses)										(308)	317	609
Net derivative gains (losses)										(590)	(690)	629
Revenues		15,840	16,171	15,333	14,964	12,387	15,806	16,349	16,245	62,308	60,787	61,343
Policyholder benefits and claims										38,313	36,358	35,144
Other expenses										13,621	13,749	14,777
Total expenses		14,879	15,686	14,315	13,892	14,058	14,717	13,979	13,752	58,772	56,506	55,692
Income (loss) from continuing operations before provision for income tax										3,536	4,281	5,651
Provision for income tax expense (benefit)										(1,470)	693	1,590
Income (loss) from continuing operations, net of income tax		2,315	883	856	952	(971)	973	1,686	1,900	5,006	3,588	4,061
Income (loss) from discontinued operations, net of income tax		0	(968)	58	(76)	(1,370)	(435)	(1,361)	432	(986)	(2,734)	1,324
Net income (loss)		2,315	(85)	914	876	(2,341)	538	325	2,332	4,020	854	5,385
Net income (loss) attributable to MetLife, Inc.		2,317	(91)	911	873	(2,343)	542	321	2,330	4,010	850	5,373
Net Income (Loss) Available to Common Stockholders, Basic		$ 2,272	$ (97)	$ 865	$ 867	$ (2,388)	$ 536	$ 275	$ 2,324	$ 3,907	$ 747	$ 5,215
Basic		$ 2.16	$ 0.82	$ 0.76	$ 0.87	$ (0.92)	$ 0.88	$ 1.49	$ 1.72	$ 4.57	$ 3.16	$ 3.48
Diluted		2.14	0.81	0.75	0.86	(0.92)	0.87	1.48	1.71	4.53	3.13	3.44
Basic		2.16	(0.09)	0.81	0.80	(2.17)	0.49	0.25	2.11	3.65	0.68	4.67
Diluted		$ 2.14	$ (0.09)	$ 0.80	$ 0.79	$ (2.17)	$ 0.48	$ 0.25	$ 2.10	$ 3.62	$ 0.67	$ 4.62
Statement of Comprehensive Income [Abstract]
Net income (loss)		$ 2,315	$ (85)	$ 914	$ 876	$ (2,341)	$ 538	$ 325	$ 2,332	$ 4,020	$ 854	$ 5,385
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax										4,623	796	(7,449)
Other Comprehensive Income (Loss), before Tax										4,369	1,137	(8,130)
Other Comprehensive Income (Loss), Tax										(984)	(450)	2,203
Other Comprehensive Income (Loss), Net of Tax										3,385	687	(5,927)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest										7,405	1,541	(542)
Comprehensive income (loss)										7,391	1,449	(574)
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)		26,527				34,683				26,527	34,683	35,672	32,110
Net income (loss)		2,317	(91)	911	873	(2,343)	542	321	2,330	4,010	850	5,373
Accumulated Other Comprehensive Income (Loss), Net of Tax		7,427				5,366				7,427	5,366	4,767	10,714
Other Comprehensive Income (Loss), Net of Tax										3,385	687	(5,927)
Stockholders' Equity Attributable to Parent		58,676				67,531				58,676	67,531	68,098	72,208
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		58,870				67,702				58,870	67,702	68,568	72,715
Statement of Cash Flows [Abstract]
Net income (loss)		2,315	(85)	914	876	(2,341)	538	325	2,332	4,020	854	5,385
(Gains) losses on investments and from sales of businesses, net										363	(183)	(560)
(Gains) losses on derivatives, net										3,610	8,779	1,371
Universal life and investment-type product policy fees										(7,708)	(9,207)	(9,507)
Change in premiums, reinsurance and other receivables										(991)	(2,158)	(831)
Increase (Decrease) in Deferred Policy Acquisition Costs										(693)	(937)	488
Increase (Decrease) in Income Taxes Payable										(2,796)	(1,522)	715
Increase (Decrease) in Insurance Liabilities										8,511	6,321	6,408
Increase (Decrease) in Other Operating Liabilities										1,603	2,801	1,172
Other, net										184	139	94
Scenario, Previously Reported
Restatement of Prior Year Income [Abstract]
Income (loss) from continuing operations before provision for income tax											4,140	5,708
Provision for income tax expense (benefit)											666	1,700
Income (loss) from continuing operations, net of income tax		2,134	893	829	908	(795)	1,024	1,475	1,770		3,474	4,008
Income (loss) from discontinued operations, net of income tax		0	(968)	58	(79)	(1,291)	(451)	(1,361)	433		(2,670)	1,314
Net Income (Loss) Available to Common Stockholders, Basic		2,091	(87)	838	820	(2,133)	571	64	2,195		697	5,152
Balance Sheet Related Disclosures [Abstract]
Future policy benefits						166,701					166,701
Policyholder account balances						173,168					173,168
Other Policy-Related Balances						13,030					13,030
Deferred Tax Liabilities, Net						6,774					6,774
Other Liabilities						23,700					23,700
Liabilities						831,284					831,284
Retained Earnings (Accumulated Deficit)						34,480					34,480	35,519	32,020
Accumulated Other Comprehensive Income (Loss), Net of Tax						5,347					5,347
Stockholders' Equity Attributable to Parent						67,309					67,309	67,949	72,053
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest						67,480					67,480	68,419	72,560
Income Statement Related Disclosures [Abstract]
Insurance Commissions and Fees											5,482	5,570
Net Investment Income											16,790	16,243
Other net investment gains (losses)											412	705
Net investment gains (losses)											305	646
Net derivative gains (losses)											(874)	545
Revenues		15,754	16,104	15,286	14,925	12,635	15,833	16,025	16,097		60,590	61,334
Policyholder benefits and claims											36,316	35,102
Other expenses											13,735	14,753
Total expenses		14,879	15,603	14,309	13,921	14,017	14,674	13,979	13,780		56,450	55,626
Income (loss) from continuing operations before provision for income tax											4,140	5,708
Provision for income tax expense (benefit)											666	1,700
Income (loss) from continuing operations, net of income tax		2,134	893	829	908	(795)	1,024	1,475	1,770		3,474	4,008
Income (loss) from discontinued operations, net of income tax		0	(968)	58	(79)	(1,291)	(451)	(1,361)	433		(2,670)	1,314
Net income (loss)		2,134	(75)	887	829	(2,086)	573	114	2,203		804	5,322
Net income (loss) attributable to MetLife, Inc.		2,136	(81)	884	826	(2,088)	577	110	2,201		800	5,310
Net Income (Loss) Available to Common Stockholders, Basic		$ 2,091	$ (87)	$ 838	$ 820	$ (2,133)	$ 571	$ 64	$ 2,195		$ 697	$ 5,152
Basic		$ 1.99	$ 0.83	$ 0.73	$ 0.82	$ (0.77)	$ 0.93	$ 1.30	$ 1.60		$ 3.06	$ 3.43
Diluted		1.97	0.82	0.72	0.82	(0.77)	0.92	1.29	1.59		3.04	3.40
Basic		1.99	(0.08)	0.78	0.75	(1.94)	0.52	0.06	1.99		0.63	4.61
Diluted		$ 1.97	$ (0.08)	$ 0.77	$ 0.75	$ (1.94)	$ 0.51	$ 0.06	$ 1.98		$ 0.63	$ 4.57
Statement of Comprehensive Income [Abstract]
Net income (loss)		$ 2,134	$ (75)	$ 887	$ 829	$ (2,086)	$ 573	$ 114	$ 2,203		$ 804	$ 5,322
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax											760	(7,443)
Other Comprehensive Income (Loss), before Tax											1,101	(8,124)
Other Comprehensive Income (Loss), Tax											(437)	2,266
Other Comprehensive Income (Loss), Net of Tax											664	(5,858)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest											1,468	(536)
Comprehensive income (loss)											1,376	(568)
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)						34,480					34,480	35,519	32,020
Net income (loss)		2,136	(81)	884	826	(2,088)	577	110	2,201		800	5,310
Accumulated Other Comprehensive Income (Loss), Net of Tax						5,347					5,347
Other Comprehensive Income (Loss), Net of Tax											664	(5,858)
Stockholders' Equity Attributable to Parent						67,309					67,309	67,949	72,053
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest						67,480					67,480	68,419	72,560
Statement of Cash Flows [Abstract]
Net income (loss)		2,134	(75)	887	829	(2,086)	573	114	2,203		804	5,322
(Gains) losses on investments and from sales of businesses, net											(171)	(597)
(Gains) losses on derivatives, net											8,963	1,451
Universal life and investment-type product policy fees											(9,206)	(9,507)
Change in premiums, reinsurance and other receivables											(2,125)	(837)
Increase (Decrease) in Deferred Policy Acquisition Costs											(949)	491
Increase (Decrease) in Income Taxes Payable											(1,557)	825
Increase (Decrease) in Insurance Liabilities											6,279	6,366
Increase (Decrease) in Other Operating Liabilities											2,766	1,134
Other, net											136	164
Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Reserves for Group Annuity products		372
Assumed variable annuity guarantee reserves		682
Restatement of Prior Year Income [Abstract]
Assumed variable annuity guarantee reserves		682
Reserves for Group Annuity products		372
Income (loss) from continuing operations before provision for income tax											141	(57)
Provision for income tax expense (benefit)											27	(110)
Income (loss) from continuing operations, net of income tax		181	(10)	27	44	(176)	(51)	211	130		114	53
Income (loss) from discontinued operations, net of income tax		0	0	0	3	(79)	16	0	(1)		(64)	10
Net Income (Loss) Available to Common Stockholders, Basic		181	(10)	27	47	(255)	(35)	211	129		50	63
Balance Sheet Related Disclosures [Abstract]
Future policy benefits						(65)					(65)
Policyholder account balances						(682)					(682)
Other Policy-Related Balances						372					372
Deferred Tax Liabilities, Net						118					118
Other Liabilities						35					35
Liabilities						(222)					(222)
Retained Earnings (Accumulated Deficit)						203					203	153	90
Accumulated Other Comprehensive Income (Loss), Net of Tax						19					19
Stockholders' Equity Attributable to Parent						222					222	149	155
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest						222					222	149	155
Income Statement Related Disclosures [Abstract]
Insurance Commissions and Fees											1	0
Net Investment Income											0	(38)
Other net investment gains (losses)											12	(37)
Net investment gains (losses)											12	(37)
Net derivative gains (losses)											184	84
Revenues		86	67	47	39	(248)	(27)	324	148		197	9
Policyholder benefits and claims											42	42
Other expenses											14	24
Total expenses		0	83	6	(29)	41	43	0	(28)		56	66
Income (loss) from continuing operations before provision for income tax											141	(57)
Provision for income tax expense (benefit)											27	(110)
Income (loss) from continuing operations, net of income tax		181	(10)	27	44	(176)	(51)	211	130		114	53
Income (loss) from discontinued operations, net of income tax		0	0	0	3	(79)	16	0	(1)		(64)	10
Net income (loss)		181	(10)	27	47	(255)	(35)	211	129		50	63
Net income (loss) attributable to MetLife, Inc.		181	(10)	27	47	(255)	(35)	211	129		50	63
Net Income (Loss) Available to Common Stockholders, Basic		$ 181	$ (10)	$ 27	$ 47	$ (255)	$ (35)	$ 211	$ 129		$ 50	$ 63
Basic		$ 0.17	$ (0.01)	$ 0.03	$ 0.05	$ (0.15)	$ (0.05)	$ 0.19	$ 0.12		$ 0.10	$ 0.05
Diluted		0.17	(0.01)	0.03	0.04	(0.15)	(0.05)	0.19	0.12		0.09	0.04
Basic		0.17	(0.01)	0.03	0.05	(0.23)	(0.03)	0.19	0.12		0.05	0.06
Diluted		$ 0.17	$ (0.01)	$ 0.03	$ 0.04	$ (0.23)	$ (0.03)	$ 0.19	$ 0.12		$ 0.04	$ 0.05
Statement of Comprehensive Income [Abstract]
Net income (loss)		$ 181	$ (10)	$ 27	$ 47	$ (255)	$ (35)	$ 211	$ 129		$ 50	$ 63
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax											36	(6)
Other Comprehensive Income (Loss), before Tax											36	(6)
Other Comprehensive Income (Loss), Tax											(13)	(63)
Other Comprehensive Income (Loss), Net of Tax											23	(69)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest											73	(6)
Comprehensive income (loss)											73	(6)
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)						203					203	153	90
Net income (loss)		181	(10)	27	47	(255)	(35)	211	129		50	63
Accumulated Other Comprehensive Income (Loss), Net of Tax						19					19
Other Comprehensive Income (Loss), Net of Tax											23	(69)
Stockholders' Equity Attributable to Parent						222					222	149	155
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest						222					222	149	155
Statement of Cash Flows [Abstract]
Net income (loss)		181	$ (10)	$ 27	$ 47	(255)	$ (35)	$ 211	$ 129		50	63
(Gains) losses on investments and from sales of businesses, net											(12)	37
(Gains) losses on derivatives, net											(184)	(80)
Universal life and investment-type product policy fees											(1)	0
Change in premiums, reinsurance and other receivables											(33)	6
Increase (Decrease) in Deferred Policy Acquisition Costs											12	(3)
Increase (Decrease) in Income Taxes Payable											35	(110)
Increase (Decrease) in Insurance Liabilities											42	42
Increase (Decrease) in Other Operating Liabilities											35	38
Other, net											56	7
Excludes impact of ASU 2016-09 [Member]
Statement of Cash Flows [Abstract]
Other, net	[1]										192	171
AOCI Attributable to Parent [Member]
Balance Sheet Related Disclosures [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax						5,366					5,366	4,767	10,714
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		7,427				5,366				7,427	5,366	4,767	10,714
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Net of Tax										3,381	599	(5,947)	(5,947)
Statement of Stockholders' Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax						5,366					5,366	4,767	10,714
Other Comprehensive Income (Loss), Net of Tax										3,381	599	(5,947)	(5,947)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 7,427				5,366				$ 7,427	5,366	4,767	10,714
AOCI Attributable to Parent [Member] | Scenario, Previously Reported
Balance Sheet Related Disclosures [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax						5,347					5,347	4,771	10,649
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest													10,649
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Net of Tax												576	(5,878)
Statement of Stockholders' Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax						5,347					5,347	4,771	10,649
Other Comprehensive Income (Loss), Net of Tax												576	(5,878)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest													10,649
AOCI Attributable to Parent [Member] | Restatement Adjustment
Balance Sheet Related Disclosures [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax						19					19	(4)	65
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest													65
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Net of Tax												23	(69)
Statement of Stockholders' Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax						$ 19					19	(4)	65
Other Comprehensive Income (Loss), Net of Tax												23	(69)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest													$ 65
Accounting Standards Update 2016-09 [Member]
Statement of Cash Flows [Abstract]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Cash Flow - Operating Activities											53	77
Restatement impact in Net Income (loss)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Reserves for Group Annuity products											(33)	(31)
Assumed variable annuity guarantee reserves											184	80
Restatement of Prior Year Income [Abstract]
Assumed variable annuity guarantee reserves											184	80
Reserves for Group Annuity products											(33)	(31)
Other revisions to continuing operations, net											(10)	(106)
Income (loss) from continuing operations before provision for income tax											141	(57)
Provision for income tax expense (benefit)											27	(110)
Income (loss) from continuing operations, net of income tax											114	53
Income (loss) from discontinued operations, net of income tax											(64)	10
Net Income (Loss) Available to Common Stockholders, Basic											50	63
Income Statement Related Disclosures [Abstract]
Income (loss) from continuing operations before provision for income tax											141	(57)
Provision for income tax expense (benefit)											27	(110)
Income (loss) from continuing operations, net of income tax											114	53
Income (loss) from discontinued operations, net of income tax											(64)	10
Net Income (Loss) Available to Common Stockholders, Basic											$ 50	$ 63

[1] Excludes impact related to adoption during 2017 of stock-based compensation guidance which decreased Other, net by $53 million and $77 million for the years ended December 31, 2016 and 2015, respectively. See “— Adoption of New Accounting Pronouncements.”