Risk Management Activities (Schedule of Cash Flow Hedges in AOCI) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net current-period other comprehensive income (loss)	$ 3.2	$ 3.5	$ 89.7
Interest rate risk programs
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net current-period other comprehensive income (loss)	$ (0.4)

Amount after tax and reclassification adjustments of other comprehensive income (loss).

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+ Details