| Document and Entity Information | Aug. 26, 2021 |
| Document and Entity Information | |
| Document Type | 8-K |
| Document Period End Date | Aug. 26, 2021 |
| Entity File Number | 001-38373 |
| Entity Registrant Name | TRANSOCEAN LTD |
| Entity Incorporation, State or Country Code | V8 |
| Entity Tax Identification Number | 98-0599916 |
| Entity Address, Address Line One | Turmstrasse 30 |
| Entity Address, City or Town | Steinhausen |
| Entity Address, Postal Zip Code | CH-6312 |
| Entity Address, Country | CH |
| City Area Code | +41 (41) |
| Local Phone Number | 749-0500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001451505 |
| Amendment Flag | false |
| Shares | |
| Document and Entity Information | |
| Title of 12(b) Security | Shares |
| Trading Symbol | RIG |
| Security Exchange Name | NYSE |
| 0.50% Exchangeable Bonds due January 2023 | |
| Document and Entity Information | |
| Title of 12(b) Security | 0.50% Exchangeable Senior Bonds due 2023 |
| Trading Symbol | RIG/23 |
| Security Exchange Name | NYSE |
