| Document and Entity Information | Aug. 20, 2021 |
| Document And Entity Information [Line Items] | |
| Entity Registrant Name | RMG Acquisition Corp. II |
| Amendment Flag | false |
| Entity Central Index Key | 0001820143 |
| Current Fiscal Year End Date | --12-31 |
| Document Type | 8-K |
| Document Period End Date | Aug. 20, 2021 |
| Entity Incorporation State Country Code | E9 |
| Entity File Number | 001-39776 |
| Entity Tax Identification Number | 98-1550286 |
| Entity Address, Address Line One | 57 Ocean |
| Entity Address, Address Line Two | Suite 403 |
| Entity Address, Address Line Three | 5775 Collins Avenue |
| Entity Address, City or Town | Miami Beach |
| Entity Address, State or Province | FL |
| Entity Address, Postal Zip Code | 33140 |
| City Area Code | (786) |
| Local Phone Number | 584-8352 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Units Each Consisting Of One Class A Ordinary Share And One Third Of One Redeemable Warrant 2 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Units, each consisting of one Class A ordinary share and one-third of one redeemable warrant |
| Trading Symbol | RMGBU |
| Security Exchange Name | NASDAQ |
| Class A Ordinary Shares Subject To Possible Redemption [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Class A ordinary shares, par value $0.0001 per share |
| Trading Symbol | RMGB |
| Security Exchange Name | NASDAQ |
| Redeemable Warrants Each Whole Warrant Exercisable For One Class A Ordinary Share At An Exercise Price Of 11.501 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Redeemable warrants, each whole warrant exercisable for one Class A ordinary share at an exercise price of $11.50 |
| Trading Symbol | RMGBW |
| Security Exchange Name | NASDAQ |
