Income Tax Expense - Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Deferred Income Tax Assets
Deferred Gain - Land Sales	$ 16.5	$ 8.3
Employee Benefits and Compensation	20.5	29.3
Property-Related	52.0	58.1
NOL Carryforwards	10.6	13.0
Tax Credit Carryforwards	486.9	557.4
Power Sales Agreements	7.3	9.0
Regulatory Liabilities	84.0	89.0
Other	4.2	0.6
Gross Deferred Income Tax Assets	682.0	764.7
Deferred Income Tax Asset Valuation Allowance	(44.9)	(58.0)
Total Deferred Income Tax Assets	637.1	706.7
Deferred Income Tax Liabilities
Deferred Gain	7.1	7.9
Property-Related	619.7	632.0
Regulatory Asset for Benefit Obligations	46.0	48.1
Unamortized Investment Tax Credits	29.0	29.6
Partnership Basis Differences	164.3	156.5
Regulatory Assets	24.4	25.3
Total Deferred Income Tax Liabilities	890.5	899.4
Net Deferred Income Taxes	$ 253.4	$ 192.7

Deferred Tax Assets, Deferred Gain Land Sales

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Deferred Tax Assets, Regulatory Liabilities

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Deferred Tax Liabilities - Deferred Gain

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Deferred Tax Liabilities, Regulatory Assets for Benefit Obligations

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Deferred Tax Liability, Partnership Basis Differences

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Power Purchase Agreements, Deferred Tax Asset

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The noncurrent portion of the reserve for accumulated deferred investment tax credits as of the balance sheet date. This is the remaining investment credit, which will reduce the cost of services collected from ratepayers by a ratable portion over the investment's regulatory life.

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Amount of deferred tax liability attributable to taxable temporary differences.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences, classified as other.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from property, plant, and equipment.

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Amount, before allocation of a valuation allowances, of deferred tax assets attributable to deductible tax credit carryforwards including, but not limited to, research, foreign, general business, alternative minimum tax, and other deductible tax credit carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from employee compensation.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences without jurisdictional netting.

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Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment.

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Amount of deferred tax liability attributable to taxable temporary differences from regulatory assets.

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