| Document and Entity Information | Aug. 16, 2021 |
| Document And Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Aug. 16, 2021 |
| Entity Registrant Name | M3-Brigade Acquisition II Corp. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-40162 |
| Entity Tax Identification Number | 86-1359752 |
| Entity Address, Address Line One | 1700 Broadway—19th Floor |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10019 |
| City Area Code | 212 |
| Local Phone Number | 202-2200 |
| Written Communications | false |
| Soliciting Material | true |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001839175 |
| Class A Ordinary Shares included as part of the units [Member] | |
| Document And Entity Information [Line Items] | |
| Title of 12(b) Security | Class A Ordinary Shares included as part of the units |
| Trading Symbol | MBAC |
| Security Exchange Name | NYSE |
| Redeemable warrants included as part of the units, each whole warrant exercisable for one Class A Ordinary Share at an exercise price of $11.50 [Member] | |
| Document And Entity Information [Line Items] | |
| Title of 12(b) Security | Redeemable warrants included as part of the units, each whole warrant exercisable for one Class A Ordinary Share at an exercise price of $11.50 |
| Trading Symbol | MBAC.WS |
| Security Exchange Name | NYSE |
| Units, each consisting of one share of Class A Ordinary Share, $0.0001 par value, and one-third of one redeemable warrant [Member] | |
| Document And Entity Information [Line Items] | |
| Title of 12(b) Security | Units, each consisting of one share of Class A Ordinary Share, $0.0001 par value, and one-third of one redeemable warrant |
| Trading Symbol | MBAC.U |
| Security Exchange Name | NYSE |
