| Document and Entity Information | Oct. 15, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | HOLOGIC INC |
| Entity Incorporation State Country Code | DE |
| Amendment Flag | false |
| Entity Central Index Key | 0000859737 |
| Document Type | 8-K |
| Document Period End Date | Oct. 15, 2020 |
| Entity File Number | 1-36214 |
| Entity Tax Identification Number | 04-2902449 |
| Entity Address, Address Line One | 250 Campus Drive |
| Entity Address, City or Town | Marlborough |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 01752 |
| City Area Code | (508) |
| Local Phone Number | 263-2900 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $.01 par value |
| Trading Symbol | HOLX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
