Deferred Policy Acquisition Costs, Value of Business Acquired and Other Policy-Related Intangibles (Negative VOBA) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite Lived Intangible Liabilities
Balance at January 1,	$ 2,162met_FiniteLivedIntangibleLiabilitiesNet	$ 2,916met_FiniteLivedIntangibleLiabilitiesNet	$ 3,657met_FiniteLivedIntangibleLiabilitiesNet
Acquisitions	0	0	10
Amortization of negative VOBA	(442)	(579)	(622)
Effect of foreign currency translation and other	(124)	(175)	(129)
Balance at December 31,	1,596met_FiniteLivedIntangibleLiabilitiesNet	2,162met_FiniteLivedIntangibleLiabilitiesNet	2,916met_FiniteLivedIntangibleLiabilitiesNet
Accumulated amortization	$ 2,404	$ 1,962	$ 1,383

- Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Accumulated amount of amortization of liabilities, excluding financial liabilities, lacking physical substance with a finite life.

+ References

No definition available.

+ Details

Name:	met_FiniteLivedIntangibleLiabilitiesAccumulatedAmortization
Namespace Prefix:	met_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The aggregate amount of the negative value of business acquired in the period and allocated to the reportable segment. The value is stated at fair value based on the purchase price allocation.

+ References

No definition available.

+ Details

Name:	met_FiniteLivedIntangibleLiabilitiesAcquiredDuringPeriod
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of the increase (decrease) during the period in negative value of business acquired liabilities due to foreign currency translation.

+ References

No definition available.

+ Details

Name:	met_FiniteLivedIntangibleLiabilitiesForeignCurrencyTranslation
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The carrying amount of the estimated fair value of the in-force contract obligations that exceeded the assumed in-force insurance policy liabilities as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	met_FiniteLivedIntangibleLiabilitiesNet
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Negative value of business acquired is amortized over the policy period reflecting the expected pattern of losses included in the liability. Such amortization is recorded in other expenses.

+ References

No definition available.

+ Details

Name:	met_NegativeValueOfBusinessAcquiredAmortization
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration