Business Segment Information (Narrative) (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2026 USD ($) segment	Jun. 30, 2025 USD ($)
Segment Reporting [Abstract]
Primary business segments \| segment			2
Segment Reporting [Line Items]
Primary business segments \| segment			2
Regulated Operating Revenue	$ 1,342.4	$ 1,283.0	$ 3,705.5	$ 3,466.2
Operating Income (Loss)	228.1	262.9	1,047.3	1,022.3
Corporate and Other
Segment Reporting [Line Items]
Regulated Operating Revenue	163.4	144.6	310.7	290.0
Operating Income (Loss)	4.4	6.7	2.8	8.4
Eliminations
Segment Reporting [Line Items]
Regulated Operating Revenue	$ (165.7)	$ (147.1)	$ (315.3)	$ (294.8)

The net result for the period of deducting operating expenses from operating revenues.

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+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details