Supplementary Financial Information - Accrued Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Offsetting [Abstract]
Accrued expenses and other current liabilities	$ 38.9	$ 27.9
Accrued payroll and employee benefits	41.3	34.7
Accrued interest	19.5	13.9
Accrued income taxes	0.0	0.6
Total accrued liabilities	$ 99.7	$ 77.1

Carrying amount as of the balance sheet date of the unpaid sum of the known and estimated amounts payable to satisfy all domestic and foreign income tax obligations due. This amount is the total of current and noncurrent accrued income taxes.

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Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Total of the carrying values as of the balance sheet date of obligations incurred through that date and payable for obligations related to services received from employees, such as accrued salaries and bonuses, payroll taxes and fringe benefits.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount of interest payable on debt, including, but not limited to, trade payables.

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Amount of expenses incurred but not yet paid classified as other.

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