Investments (Repurchase Agreement - Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Offsetting Assets [Line Items]
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	$ 117
Receivable Under Reverse Repurchase Agreements	499
Payable Under Repurchase Agreements	499met_PayableUnderRepurchaseAgreements
Amount Offset in Balance Sheet	499met_AmountOffsetinBalanceSheet
Maximum
Offsetting Assets [Line Items]
Repurchase Agreements, Interest Expense Amount	1
Net Amount Assets (Liabilities) From Repurchase, Reverse Repurchase Agreements	1
Fixed Maturity Securities
Offsetting Assets [Line Items]
Securities Loaned, Not Subject to Master Netting Arrangement	516
Securities Borrowed, Not Subject to Master Netting Arrangement	$ 505

Amount offset in balance sheet from receivables and payables under repurchase and reverse repurchase agreement.

No definition available.

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- Definition

Net amount, after affects of netting, from repurchase and reverse repurchase agreements presented on the Balance sheet.

+ References

No definition available.

+ Details

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- Definition

The gross amounts payable under repurchase agreement.

+ References

No definition available.

+ Details

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- Definition

The gross amounts of those recognized receivable under reverse repurchase agreements.

+ References

No definition available.

+ Details

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- Definition

Fair value of the collateral, or portion thereof, that has been re-pledged, delivered, or otherwise used.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=34720971&loc=SL6224234-111729

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- Definition

This is the amount of interest expense incurred during the reporting period as a result of repurchase agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.7)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 405

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35710549&loc=d3e44076-110983

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 9

+ Details

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- Definition

Amount of securities borrowed from entities in exchange for collateral, not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 22

-URI http://asc.fasb.org/extlink&oid=36459792&loc=SL20226052-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=34720828&loc=SL20225862-175312

+ Details

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- Definition

Amount of securities loaned to entities in exchange for collateral, not subject to a master netting arrangement.

+ References

+ Details

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