| Document and Entity Information Document | May 14, 2021 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | May 14, 2021 |
| Entity Registrant Name | METLIFE, INC. |
| Entity Central Index Key | 0001099219 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 1-15787 |
| Entity Tax Identification Number | 13-4075851 |
| Entity Address, Address Line One | 200 Park Avenue, |
| Entity Address, City or Town | New York, |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10166-0188 |
| City Area Code | 212 |
| Local Phone Number | 578-9500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Common Stock, par value $0.01 |
| Trading Symbol | MET |
| Security Exchange Name | NYSE |
| Series A | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Floating Rate Non-Cumulative Preferred Stock,Series A, par value $0.01 |
| Trading Symbol | MET PRA |
| Security Exchange Name | NYSE |
| Series E Preferred Stock | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Depositary Shares, each representing a 1/1,000thinterest in a share of 5.625% Non-Cumulative Preferred Stock, Series E |
| Trading Symbol | MET PRE |
| Security Exchange Name | NYSE |
| Series F Preferred Stock [Member] | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Depositary Shares, each representing a 1/1,000thinterest in a share of 4.75% Non-CumulativePreferred Stock, Series F |
| Trading Symbol | MET PRF |
| Security Exchange Name | NYSE |
