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Acquisition of Versant Health Narrative (Details) | 12 Months Ended
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Dec. 31, 2020
Versant Health, Inc. [Member] | Maximum |
Business Acquisition [Line Items] |
Versant Health total revenue | 2.00%

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- Definition Versant Health total revenue + References No definition available. + Details
Name: | met_VersantHealthTotalRevenue
Namespace Prefix: | met_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_BusinessAcquisitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_BusinessAcquisitionAxis=met_VersantHealthIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |