Other Comprehensive Income: Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	$ (14.8)	$ (15.6)
Other comprehensive income (loss), before reclassifications	(0.2)	(0.7)
Amounts reclassified from AOCI	3.7	3.0
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(11.3)	(13.3)
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	(6.2)	(6.1)
Other comprehensive income (loss), before reclassifications	0.0	0.0
Amounts reclassified from AOCI	0.1	0.0
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(6.1)	(6.1)
Interest Rate Swap | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	(6.1)	(8.3)
Other comprehensive income (loss), before reclassifications	0.0	0.0
Amounts reclassified from AOCI	1.1	1.1
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	(5.0)	(7.2)
Commodity Contract | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start	(2.5)	(1.2)
Other comprehensive income (loss), before reclassifications	(0.2)	(0.7)
Amounts reclassified from AOCI	2.5	1.9
Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End	$ (0.2)	$ 0.0