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Fair Value Measurements (Fair Value Inputs, Liabilities, Quantitative Information) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Fair Value Inputs, Liabilities, Quantitative Information
Long-term debt	$ 1,033.7	$ 1,033.4
Long-term debt, fair value	$ 1,000.0
Level 1 Inputs
Fair Value Inputs, Liabilities, Quantitative Information
Fair value level 1 inputs	quoted prices in active markets for identical liabilities (Level 1 inputs

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Fair value level 1 inputs

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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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- 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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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.

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