Basis of presentation (Details) - Discontinued Operations, Disposed of by Means Other than Sale, Spinoff - Knife River Corporation shares in Millions	May 31, 2023 shares
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pro rata distribution of shares, percentage	0.90
Stock split, conversion ratio	4
Retained ownership percentage	0.10
Number of retained shares (in shares)	5.7