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
	Mar. 31, 2018	Mar. 31, 2017	Dec. 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]
Other net investment gains (losses)		$ 88
Net investment gains (losses)	$ (333)	88
Net derivative gains (losses)	349	(212)
Revenues	14,805	14,964
Policyholder benefits and claims	8,718	8,863
Other expenses	3,365	3,268
Total expenses	13,149	13,892
Income (loss) from continuing operations before provision for income tax	1,656	1,072
Provision for income tax expense (benefit)	399	120
Income (loss) from continuing operations, net of income tax	1,257	952
Income (loss) from discontinued operations, net of income tax	0	(76)
Net income (loss)	1,257	876
Net income (loss) attributable to MetLife, Inc.	1,253	873
Net Income (Loss) Available to Common Stockholders, Basic	1,247	867
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(1,448)	1,907
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ (1,452)	$ 1,903
Income (loss) from continuing operations, net of tax - Basic	$ 1.20	$ 0.87
Income (loss) from continuing operations, net of tax - Diluted	1.19	0.86
Income (loss) per common share - Basic	1.20	0.80
Income (loss) per common share - Diluted	$ 1.19	$ 0.79
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)	$ 26,453	$ 35,113	26,527	$ 34,683
Net income (loss)	1,253	873
Accumulated Other Comprehensive Income (Loss), Net of Tax	5,634	6,396	7,427	5,366
Other Comprehensive Income (Loss), Net of Tax	(2,705)	1,031
Stockholders' Equity Attributable to Parent	56,310	68,179	58,676	67,531
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	56,508	68,358	58,870	67,702
Discontinued Operations
Income Statement Related Disclosures [Abstract]
Net investment gains (losses)		5
Provision for income tax expense (benefit)		2
Scenario, Previously Reported
Income Statement Related Disclosures [Abstract]
Other net investment gains (losses)		8
Net investment gains (losses)		8
Net derivative gains (losses)		(926)
Revenues		16,269
Policyholder benefits and claims		9,859
Other expenses		3,564
Total expenses		15,452
Income (loss) from continuing operations before provision for income tax		817
Provision for income tax expense (benefit)		(12)
Income (loss) from continuing operations, net of income tax		829
Income (loss) from discontinued operations, net of income tax		0
Net income (loss)		829
Net income (loss) attributable to MetLife, Inc.		826
Net Income (Loss) Available to Common Stockholders, Basic		820
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		1,879
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		$ 1,875
Income (loss) from continuing operations, net of tax - Basic		$ 0.75
Income (loss) from continuing operations, net of tax - Diluted		0.75
Income (loss) per common share - Basic		0.75
Income (loss) per common share - Diluted		$ 0.75
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)		$ 34,863		34,480
Net income (loss)		826
Stockholders' Equity Attributable to Parent		67,929		67,309
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		68,108		67,480
Restatement Adjustment
Income Statement Related Disclosures [Abstract]
Other net investment gains (losses)		25
Net investment gains (losses)		25
Net derivative gains (losses)		14
Revenues		39
Policyholder benefits and claims		6
Other expenses		(35)
Total expenses		(29)
Income (loss) from continuing operations before provision for income tax		68
Provision for income tax expense (benefit)		24
Income (loss) from continuing operations, net of income tax		44
Income (loss) from discontinued operations, net of income tax		3
Net income (loss)		47
Net income (loss) attributable to MetLife, Inc.		47
Net Income (Loss) Available to Common Stockholders, Basic		47
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		28
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		$ 28
Income (loss) from continuing operations, net of tax - Basic		$ 0.05
Income (loss) from continuing operations, net of tax - Diluted		0.04
Income (loss) per common share - Basic		0.05
Income (loss) per common share - Diluted		$ 0.04
Statement of Stockholders' Equity [Abstract]
Retained Earnings (Accumulated Deficit)		$ 250		203
Net income (loss)		47
Stockholders' Equity Attributable to Parent		250		222
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		250		222
Restatement Adjustment | Discontinued Operations
Income Statement Related Disclosures [Abstract]
Other net investment gains (losses)		55
Net investment gains (losses)		55
Net derivative gains (losses)		700
Revenues		(1,344)
Policyholder benefits and claims		(1,002)
Other expenses		(261)
Total expenses		(1,531)
Income (loss) from continuing operations before provision for income tax		187
Provision for income tax expense (benefit)		108
Income (loss) from continuing operations, net of income tax		79
Income (loss) from discontinued operations, net of income tax		(79)
Net income (loss)		0
Net income (loss) attributable to MetLife, Inc.		0
Net Income (Loss) Available to Common Stockholders, Basic		0
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		0
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		$ 0
Income (loss) from continuing operations, net of tax - Basic		$ 0.07
Income (loss) from continuing operations, net of tax - Diluted		0.07
Income (loss) per common share - Basic		0.00
Income (loss) per common share - Diluted		$ 0.00
Statement of Stockholders' Equity [Abstract]
Net income (loss)		$ 0
AOCI Attributable to Parent
Statement of Stockholders' Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax		6,396		5,366
Other Comprehensive Income (Loss), Net of Tax	(2,705)	1,030
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 5,634	6,396	$ 7,427	5,366
AOCI Attributable to Parent | Scenario, Previously Reported
Statement of Stockholders' Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax		6,396		5,347
Other Comprehensive Income (Loss), Net of Tax		1,049
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest				5,347
AOCI Attributable to Parent | Restatement Adjustment
Statement of Stockholders' Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax		0		19
Other Comprehensive Income (Loss), Net of Tax		(19)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest				$ 19
Restatement impact in Net Income (loss)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Assumed variable annuity guarantee reserves		14
Reserves for Group Annuity products		(9)
Other revisions to continuing operations, net		63
Income Statement Related Disclosures [Abstract]
Income (loss) from continuing operations before provision for income tax		68
Provision for income tax expense (benefit)		24
Income (loss) from continuing operations, net of income tax		44
Income (loss) from discontinued operations, net of income tax		3
Net Income (Loss) Available to Common Stockholders, Basic		$ 47