Fair Value (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Level 1 [Member]
Total Assets	$ 7.3	$ 7.5
Level 1 [Member] \| Subsidiaries [Member]
Total Assets	7.3	7.5
Level 2 [Member]
Total Assets	0.0	0.0
Level 2 [Member] \| Subsidiaries [Member]
Total Assets	0.0	0.0
Level 3 [Member]
Total Assets	0.0	0.0
Level 3 [Member] \| Subsidiaries [Member]
Total Assets	0.0	0.0
Fair Value [Member]
Total Assets	7.3	7.5
Fair Value [Member] \| Subsidiaries [Member]
Total Assets	7.3	7.5
Money Market Funds [Member] \| Level 1 [Member]
Investments, Fair Value Disclosure	0.6	0.5
Money Market Funds [Member] \| Level 1 [Member] \| Subsidiaries [Member]
Investments, Fair Value Disclosure	0.6	0.5
Money Market Funds [Member] \| Level 2 [Member]
Investments, Fair Value Disclosure	0.0	0.0
Money Market Funds [Member] \| Level 2 [Member] \| Subsidiaries [Member]
Investments, Fair Value Disclosure	0.0	0.0
Money Market Funds [Member] \| Level 3 [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]
Investments, Fair Value Disclosure	0.6	0.5
Money Market Funds [Member] \| Fair Value [Member] \| Subsidiaries [Member]
Investments, Fair Value Disclosure	0.6	0.5
Debt [Member] \| Level 1 [Member]
Debt	0.0	0.0
Debt [Member] \| Level 1 [Member] \| Subsidiaries [Member]
Debt	0.0	0.0
Debt [Member] \| Level 2 [Member]
Debt	1,414.5	1,376.4
Debt [Member] \| Level 2 [Member] \| Subsidiaries [Member]
Debt	676.5	610.9
Debt [Member] \| Level 3 [Member]
Debt	16.9	17.0
Debt [Member] \| Level 3 [Member] \| Subsidiaries [Member]
Debt	16.9	17.0
Debt [Member] \| Fair Value [Member]
Debt	1,431.4	1,393.4
Debt [Member] \| Fair Value [Member] \| Subsidiaries [Member]
Debt	693.4	627.9
Mutual Fund \| Level 1 [Member]
Investments, Fair Value Disclosure	6.7	7.0
Mutual Fund \| Level 1 [Member] \| Subsidiaries [Member]
Investments, Fair Value Disclosure	6.7	7.0
Mutual Fund \| Level 2 [Member]
Investments, Fair Value Disclosure	0.0	0.0
Mutual Fund \| Level 2 [Member] \| Subsidiaries [Member]
Investments, Fair Value Disclosure	0.0	0.0
Mutual Fund \| Level 3 [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]
Investments, Fair Value Disclosure	6.7	7.0
Mutual Fund \| Fair Value [Member] \| Subsidiaries [Member]
Investments, Fair Value Disclosure	$ 6.7	$ 7.0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
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