Fair Value (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Long-term Debt	$ 1,426.3	$ 1,840.0
Level 1 [Member]
Total Assets	7.8	8.0
Level 2 [Member]
Total Assets	0.0	0.0
Level 3 [Member]
Total Assets	0.0	0.0
Fair Value [Member]
Total Assets	7.8	8.0
Money Market Funds [Member] | Level 1 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0.6	0.4
Money Market Funds [Member] | Level 2 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0.0	0.0
Money Market Funds [Member] | Level 3 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0.0	0.0
Money Market Funds [Member] | Fair Value [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0.6	0.4
Debt [Member] | Level 1 [Member]
Debt	0.0	0.0
Debt [Member] | Level 2 [Member]
Debt	1,301.8	1,692.4
Debt [Member] | Level 3 [Member]
Debt	16.5	16.6
Debt [Member] | Fair Value [Member]
Debt	1,318.3	1,709.0
Mutual Fund | Level 1 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	7.2	7.6
Mutual Fund | Level 2 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0.0	0.0
Mutual Fund | Level 3 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0.0	0.0
Mutual Fund | Fair Value [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	$ 7.2	$ 7.6