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Debt - Effective Interest Rate (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Debt
Effective interest rate including effects of interest rate swap agreements			4.7%	4.2%
Amortization of deferred debt issuance costs	$ 9.8	$ 8.7	$ 12.6	$ 11.5
The 2022 Notes
Debt
Prepayment premium redemption	$ 34.5		$ 34.5

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Amount of amortization expense attributable to debt issuance costs.

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-SubTopic 30
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Description of any adjustments made to the stated rate to determine the effective rate.

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