| Document and Entity Information | Jul. 06, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | CARPENTER TECHNOLOGY CORP |
| Amendment Flag | false |
| Entity Central Index Key | 0000017843 |
| Document Type | 8-K |
| Document Period End Date | Jul. 6, 2020 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 1-5828 |
| Entity Tax Identification Number | 23-0458500 |
| Entity Address, Address Line One | 1735 Market Street |
| Entity Address, City or Town | Philadelphia |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 19103 |
| City Area Code | (610) |
| Local Phone Number | 208-2000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $5 Par Value |
| Trading Symbol | CRS |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
