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Equity (Stock-Based Compensation Plans - Narrative) (Details) - shares | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2022 | Dec. 31, 2021
Minimum |  |
Equity - Stock-based Compensation Plans [Line Items] |  |
Future Performance Factor |  | 0.00%
Maximum |  |
Equity - Stock-based Compensation Plans [Line Items] |  |
Future Performance Factor |  | 175.00%
Performance Shares |  |
Equity - Stock-based Compensation Plans [Line Items] |  |
Performance Factor |  | 141.30%
Vested in period |  | 1,485,512
Issued in period | 2,099,028 |
Performance Units |  |
Equity - Stock-based Compensation Plans [Line Items] |  |
Vested in period |  | 156,090
Paid in period | 220,555 |

X
- Definition The percentage of the performance factor for the future three year performance period used for performance shares and units. + References No definition available. + Details
Name: | met_FuturePerformanceFactor
Namespace Prefix: | met_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of the performance factor for the three year performance period used for performance shares and units. + References No definition available. + Details
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Namespace Prefix: | met_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The cash value of vested performance units that was paid under a unit-based compensation plan. + References No definition available. + Details
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Namespace Prefix: | met_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(02) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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Balance Type: | na
Period Type: | duration

X
- 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
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X
- Definition Number of shares issued under share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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Balance Type: | na
Period Type: | duration

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- Details
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- Details
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- Details
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- Details
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