Risk Management and Derivatives: Cash Flow Hedges (Details) - Cash Flow Hedging - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Interest rate swaps
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			$ 3.1
Designated as Hedging Instrument
Derivative [Line Items]
Unrealized Gain (Loss) on Cash Flow Hedging Instruments	$ 1.3	$ 1.3	4.4	$ 2.9
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (1.3)	$ (1.2)	$ (4.6)	$ (3.9)
Derivative Instrument, Gain (Loss) Reclassified from AOCI into Income, Effective Portion, Statement of Income or Comprehensive Income [Extensible Enumeration]	Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest
Designated as Hedging Instrument \| Interest rate swaps
Derivative [Line Items]
Unrealized Gain (Loss) on Cash Flow Hedging Instruments	$ 0.7	$ 0.7	$ 1.4	$ 1.4
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	$ (0.7)	$ (0.7)	$ (1.4)	$ (1.4)
Derivative Instrument, Loss Reclassified from AOCI into Income, Effective Portion, Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest Costs Incurred	Interest Costs Incurred	Interest Costs Incurred	Interest Costs Incurred
Designated as Hedging Instrument \| Commodity Contract
Derivative [Line Items]
Unrealized Gain (Loss) on Cash Flow Hedging Instruments	$ 0.6	$ 0.6	$ 3.0	$ 1.5
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	$ (0.6)	$ (0.5)	$ (3.2)	$ (2.5)
Derivative Instrument, Gain Reclassified from AOCI into Income, Effective Portion, Statement of Income or Comprehensive Income [Extensible Enumeration]	Fuel, Purchased Power and Cost of Gas Sold	Fuel, Purchased Power and Cost of Gas Sold	Fuel, Purchased Power and Cost of Gas Sold	Fuel, Purchased Power and Cost of Gas Sold

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

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Indicates line item in statement of income or comprehensive income that includes gain (loss) from effective portion of derivative instrument reclassified from accumulated other comprehensive income (AOCI) into income.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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The effective portion of loss reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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Amount of unrealized gain (loss) related to derivatives designated as cash flow hedging instruments, recorded in results of operations to the extent that the cash flow hedge is determined to be ineffective.

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