| Document and Entity Information | Aug. 01, 2019 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 1, 2019 |
| Entity Registrant Name | WestRock Co |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-38736 |
| Entity Tax Identification Number | 37-1880617 |
| Entity Address, Address Line One | 1000 Abernathy Road |
| Entity Address, City or Town | Atlanta |
| Entity Address, State or Province | GA |
| Entity Address, Postal Zip Code | 30328 |
| City Area Code | 770 |
| Local Phone Number | 448-2193 |
| Entity Information, Former Legal or Registered Name | Not Applicable |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | WRK |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001732845 |
