Business, Basis of Presentation and Summary of Significant Accounting Policies (Restatement Adjustments) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Assumed variable annuity guarantee reserves					$ 896
Reserves for Group Annuity products					510
Income Statement Related Disclosures [Abstract]
Net investment gains (losses)	$ 117	$ (606)	$ (443)	$ (414)
Net derivative gains (losses)	(378)	(123)	(88)	(535)
Revenues	16,289	16,171	52,279	46,468
Policyholder benefits and claims	10,080	10,728	33,664	29,018
Other expenses	3,469	3,318	10,319	9,869
Total expenses	15,210	15,686	48,443	43,893
Income (loss) from continuing operations before provision for income tax	1,079	485	3,836	2,575
Provision for income tax expense (benefit)	164	(398)	770	(116)
Income (loss) from continuing operations, net of income tax	915	883	3,066	2,691
Income (loss) from discontinued operations, net of income tax	0	(968)	0	(986)
Net income (loss)	915	(85)	3,066	1,705
Net income (loss) attributable to MetLife, Inc.	912	(91)	3,056	1,693
Net Income (Loss) Available to Common Stockholders, Basic	880	(97)	2,972	1,635
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(940)	(192)	(4,273)	4,668
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ (942)	$ (202)	$ (4,283)	$ 4,652
Income (loss) from continuing operations, net of tax - Basic	$ 0.89	$ 0.82	$ 2.93	$ 2.44
Income (loss) from continuing operations, net of tax - Diluted	0.88	0.81	2.91	2.42
Income (loss) per common share - Basic	0.89	(0.09)	2.93	1.52
Income (loss) per common share - Diluted	$ 0.88	$ (0.09)	$ 2.91	$ 1.51
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)	$ 27,331	$ 24,677	$ 27,331	$ 24,677	26,527			$ 34,683
Net income (loss)	912	(91)	3,056	1,693
Accumulated Other Comprehensive Income (Loss), Net of Tax	1,000	7,005	1,000	7,005	7,427	$ 2,854	$ 8,436	5,366
Other Comprehensive Income (Loss), Net of Tax			(7,339)	2,963
Stockholders' Equity Attributable to Parent	51,625	56,981	51,625	56,981	58,676			67,531
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	51,809	57,211	51,809	57,211	58,870			67,702
AOCI Attributable to Parent
Statement of Stockholders' Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax		7,005		7,005				5,366
Other Comprehensive Income (Loss), Net of Tax			(7,339)	2,959
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 1,000	7,005	$ 1,000	7,005				5,366
Restatement impact in Net Income (loss)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Assumed variable annuity guarantee reserves		67		128
Reserves for Group Annuity products		(12)		(30)
Other revisions to continuing operations, net		(71)		(5)
Income Statement Related Disclosures [Abstract]
Income (loss) from continuing operations before provision for income tax		(16)		93
Provision for income tax expense (benefit)		(6)		32
Income (loss) from continuing operations, net of income tax		(10)		61
Income (loss) from discontinued operations, net of income tax		0		3
Net Income (Loss) Available to Common Stockholders, Basic		(10)		64
Previously Reported
Income Statement Related Disclosures [Abstract]
Net investment gains (losses)		(606)		(439)
Net derivative gains (losses)		(190)		(663)
Revenues		16,104		46,315
Policyholder benefits and claims		10,645		28,923
Other expenses		3,318		9,904
Total expenses		15,603		43,833
Income (loss) from continuing operations before provision for income tax		501		2,482
Provision for income tax expense (benefit)		(392)		(148)
Income (loss) from continuing operations, net of income tax		893		2,630
Income (loss) from discontinued operations, net of income tax		(968)		(989)
Net income (loss)		(75)		1,641
Net income (loss) attributable to MetLife, Inc.		(81)		1,629
Net Income (Loss) Available to Common Stockholders, Basic		(87)		1,571
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		(182)		4,623
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		$ (192)		$ 4,607
Income (loss) from continuing operations, net of tax - Basic		$ 0.83		$ 2.38
Income (loss) from continuing operations, net of tax - Diluted		0.82		2.36
Income (loss) per common share - Basic		(0.08)		1.46
Income (loss) per common share - Diluted		$ (0.08)		$ 1.45
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)		$ 24,410		$ 24,410				34,480
Net income (loss)		(81)		1,629
Stockholders' Equity Attributable to Parent		56,714		56,714				67,309
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		56,944		56,944	58,870			67,480
Previously Reported | AOCI Attributable to Parent
Statement of Stockholders' Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax		7,005		7,005				5,347
Other Comprehensive Income (Loss), Net of Tax				2,978
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest					$ 7,427			5,347
Restatement Adjustment
Income Statement Related Disclosures [Abstract]
Net investment gains (losses)		0		25
Net derivative gains (losses)		67		128
Revenues		67		153
Policyholder benefits and claims		83		95
Other expenses		0		(35)
Total expenses		83		60
Income (loss) from continuing operations before provision for income tax		(16)		93
Provision for income tax expense (benefit)		(6)		32
Income (loss) from continuing operations, net of income tax		(10)		61
Income (loss) from discontinued operations, net of income tax		0		3
Net income (loss)		(10)		64
Net income (loss) attributable to MetLife, Inc.		(10)		64
Net Income (Loss) Available to Common Stockholders, Basic		(10)		64
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		(10)		45
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		$ (10)		$ 45
Income (loss) from continuing operations, net of tax - Basic		$ (0.01)		$ 0.06
Income (loss) from continuing operations, net of tax - Diluted		(0.01)		0.06
Income (loss) per common share - Basic		(0.01)		0.06
Income (loss) per common share - Diluted		$ (0.01)		$ 0.06
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)		$ 267		$ 267				203
Net income (loss)		(10)		64
Stockholders' Equity Attributable to Parent		267		267				222
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		267		267				222
Restatement Adjustment | AOCI Attributable to Parent
Statement of Stockholders' Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax		$ 0		0				19
Other Comprehensive Income (Loss), Net of Tax				$ (19)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest								$ 19