Fair Value (Fair Value and Cost of Non-Derivative Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Long-term Debt	$ 1,536.7	$ 1,535.9
Subsidiaries [Member]
Long-term Debt	713.0	712.7
Money Market Funds [Member] \| Fair Value [Member]
Investments, Fair Value Disclosure	0.3	0.5
Money Market Funds [Member] \| Fair Value [Member] \| Subsidiaries [Member]
Investments, Fair Value Disclosure	$ 0.3	$ 0.5

Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant