Risk Management and Derivatives: Derivatives by Balance Sheet Classification (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ (2.9)	$ (1.4)
Commodity Contract | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(3.9)	(4.1)
Derivative assets, current | Commodity Contract | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.0	0.1
Derivative assets, current | Commodity Contract | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.0	0.5
Other assets, non-current | Commodity Contract | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.0	0.2
Other assets, non-current | Commodity Contract | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.0	0.3
Derivative liabilities, current | Commodity Contract | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(2.7)	(1.7)
Derivative liabilities, current | Commodity Contract | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(3.8)	(4.9)
Other deferred credits and other liabilities | Commodity Contract | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(0.2)	0.0
Other deferred credits and other liabilities | Commodity Contract | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ (0.1)	$ 0.0