Fair Value (Fair Value and Cost of Non-Derivative Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Long-term Debt	$ 1,396.0	$ 1,395.5
Subsidiaries [Member]
Long-term Debt	574.3	574.3
Cost [Member]
Total Assets	6.0	6.1
Cost [Member] \| Subsidiaries [Member]
Total Assets	6.0	6.1
Fair Value [Member]
Total Assets	8.4	9.4
Fair Value [Member] \| Subsidiaries [Member]
Total Assets	8.4	9.4
Money Market Funds [Member] \| Cost [Member]
6000000	0.4	0.4
Money Market Funds [Member] \| Cost [Member] \| Subsidiaries [Member]
6000000	0.4	0.4
Money Market Funds [Member] \| Fair Value [Member]
Investments, Fair Value Disclosure	0.4	0.4
Money Market Funds [Member] \| Fair Value [Member] \| Subsidiaries [Member]
Investments, Fair Value Disclosure	0.4	0.4
Equity Securities [Member] \| Cost [Member]
6000000	1.9	1.9
Equity Securities [Member] \| Cost [Member] \| Subsidiaries [Member]
6000000	1.9	1.9
Equity Securities [Member] \| Fair Value [Member]
Investments, Fair Value Disclosure	4.5	5.1
Equity Securities [Member] \| Fair Value [Member] \| Subsidiaries [Member]
Investments, Fair Value Disclosure	4.5	5.1
Debt Securities [Member] \| Cost [Member]
6000000	3.7	3.8
Debt Securities [Member] \| Cost [Member] \| Subsidiaries [Member]
6000000	3.7	3.8
Debt Securities [Member] \| Fair Value [Member]
Investments, Fair Value Disclosure	3.5	3.9
Debt Securities [Member] \| Fair Value [Member] \| Subsidiaries [Member]
Investments, Fair Value Disclosure	3.5	3.9
Debt [Member] \| Fair Value [Member]
Debt, Fair Value	1,403.7	1,519.7
Debt [Member] \| Fair Value [Member] \| Subsidiaries [Member]
Debt, Fair Value	$ 582.8	$ 642.6

The total of assets that are measured on a recurring basis.

No definition available.

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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-Publisher FASB
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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

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- Definition

Includes other investments and securities that are not at fair value as of the balance sheet date and those that are not accounted for under the equity method.

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