Business, Basis of Presentation and Summary of Significant Accounting Policies (Restatement Adjustments) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Mar. 31, 2018	Mar. 31, 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)	$ (227)	$ 104	$ (560)	$ 192
Net derivative gains (losses)	(59)	(200)	290	(412)
Revenues	21,185	15,333	35,990	30,297
Policyholder benefits and claims	14,866	9,427	23,584	18,290
Other expenses	3,485	3,283	6,850	6,551
Total expenses	20,084	14,315	33,233	28,207
Income (loss) from continuing operations before provision for income tax	1,101	1,018	2,757	2,090
Provision for income tax expense (benefit)	207	162	606	282
Income (loss) from continuing operations, net of income tax	894	856	2,151	1,808
Income (loss) from discontinued operations, net of income tax	0	58	0	(18)
Net income (loss)	894	914	2,151	1,790
Net income (loss) attributable to MetLife, Inc.	891	911	2,144	1,784
Net Income (Loss) Available to Common Stockholders, Basic	845	865	2,092	1,732
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(1,885)	2,953	(3,333)	4,860
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ (1,889)	$ 2,951	$ (3,341)	$ 4,854
Income (loss) from continuing operations, net of tax - Basic	$ 0.83	$ 0.76	$ 2.04	$ 1.62
Income (loss) from continuing operations, net of tax - Diluted	0.83	0.75	2.02	1.61
Income (loss) per common share - Basic	0.83	0.81	2.04	1.60
Income (loss) per common share - Diluted	$ 0.83	$ 0.80	$ 2.02	$ 1.59
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)	$ 26,870	$ 35,547	$ 26,870	$ 35,547	26,527			$ 34,683
Net income (loss)	891	911	2,144	1,784
Accumulated Other Comprehensive Income (Loss), Net of Tax	2,854	8,436	2,854	8,436	7,427	$ 5,634	$ 6,396	5,366
Other Comprehensive Income (Loss), Net of Tax			(5,484)	3,070
Stockholders' Equity Attributable to Parent	53,633	69,732	53,633	69,732	58,676			67,531
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	53,832	69,946	53,832	69,946	58,870			67,702
Discontinued Operations
Income Statement Related Disclosures [Abstract]
Net investment gains (losses)				5
Provision for income tax expense (benefit)				2
AOCI Attributable to Parent
Statement of Stockholders' Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax		8,436		8,436				5,366
Other Comprehensive Income (Loss), Net of Tax			(5,485)	3,070
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 2,854	8,436	$ 2,854	8,436				5,366
Restatement impact in Net Income (loss)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Assumed variable annuity guarantee reserves		47		61
Reserves for Group Annuity products		(9)		(18)
Other revisions to continuing operations, net		3		66
Income Statement Related Disclosures [Abstract]
Income (loss) from continuing operations before provision for income tax		41		109
Provision for income tax expense (benefit)		14		38
Income (loss) from continuing operations, net of income tax		27		71
Income (loss) from discontinued operations, net of income tax		0		3
Net Income (Loss) Available to Common Stockholders, Basic		27		74
Previously Reported
Income Statement Related Disclosures [Abstract]
Net investment gains (losses)		104		112
Net derivative gains (losses)		(437)		(1,363)
Revenues		17,245		33,514
Policyholder benefits and claims		10,302		20,161
Other expenses		4,059		7,623
Total expenses		16,243		31,695
Income (loss) from continuing operations before provision for income tax		1,002		1,819
Provision for income tax expense (benefit)		115		103
Income (loss) from continuing operations, net of income tax		887		1,716
Income (loss) from discontinued operations, net of income tax		0		0
Net income (loss)		887		1,716
Net income (loss) attributable to MetLife, Inc.		884		1,710
Net Income (Loss) Available to Common Stockholders, Basic		838		1,658
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		2,926		4,805
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		$ 2,924		$ 4,799
Income (loss) from continuing operations, net of tax - Basic		$ 0.78		$ 1.53
Income (loss) from continuing operations, net of tax - Diluted		0.77		1.52
Income (loss) per common share - Basic		0.78		1.53
Income (loss) per common share - Diluted		$ 0.77		$ 1.52
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)		$ 35,270		$ 35,270				34,480
Net income (loss)		884		1,710
Stockholders' Equity Attributable to Parent		69,455		69,455				67,309
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		69,669		69,669	58,870			67,480
Previously Reported | AOCI Attributable to Parent
Statement of Stockholders' Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax		8,436		8,436				5,347
Other Comprehensive Income (Loss), Net of Tax				3,089
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)		47		61
Revenues		47		86
Policyholder benefits and claims		6		12
Other expenses		0		(35)
Total expenses		6		(23)
Income (loss) from continuing operations before provision for income tax		41		109
Provision for income tax expense (benefit)		14		38
Income (loss) from continuing operations, net of income tax		27		71
Income (loss) from discontinued operations, net of income tax		0		3
Net income (loss)		27		74
Net income (loss) attributable to MetLife, Inc.		27		74
Net Income (Loss) Available to Common Stockholders, Basic		27		74
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		27		55
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		$ 27		$ 55
Income (loss) from continuing operations, net of tax - Basic		$ 0.03		$ 0.07
Income (loss) from continuing operations, net of tax - Diluted		0.03		0.07
Income (loss) per common share - Basic		0.03		0.07
Income (loss) per common share - Diluted		$ 0.03		$ 0.07
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)		$ 277		$ 277				203
Net income (loss)		27		74
Stockholders' Equity Attributable to Parent		277		277				222
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		277		277				222
Restatement Adjustment | Discontinued Operations
Income Statement Related Disclosures [Abstract]
Net investment gains (losses)		0		55
Net derivative gains (losses)		190		890
Revenues		(1,959)		(3,303)
Policyholder benefits and claims		(881)		(1,883)
Other expenses		(776)		(1,037)
Total expenses		(1,934)		(3,465)
Income (loss) from continuing operations before provision for income tax		(25)		162
Provision for income tax expense (benefit)		33		141
Income (loss) from continuing operations, net of income tax		(58)		21
Income (loss) from discontinued operations, net of income tax		58		(21)
Net income (loss)		0		0
Net income (loss) attributable to MetLife, Inc.		0		0
Net Income (Loss) Available to Common Stockholders, Basic		0		0
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		0		0
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		$ 0		$ 0
Income (loss) from continuing operations, net of tax - Basic		$ (0.05)		$ 0.02
Income (loss) from continuing operations, net of tax - Diluted		(0.05)		0.02
Income (loss) per common share - Basic		0.00		0.00
Income (loss) per common share - Diluted		$ 0.00		$ 0.00
Statement of Stockholders' Equity [Abstract]
Net income (loss)		$ 0		$ 0
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