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Debt - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Debt Instrument [Line Items]
Cash payments paid for interest	$ 15.8	$ 15.9
Amortization of treasury lock settlements	1.4	1.4
Amortization of deferred financing costs	0.4	$ 0.4
Deferred finance costs, net	11.9
Unsecured Debt \| Seven-Year Term Loan, due October 2020
Debt Instrument [Line Items]
Repayment of debt	$ 1.6
Debt Instrument, Term	7 years
Senior Notes \| Fixed-Rate Senior Notes
Debt Instrument [Line Items]
Book value of fixed rate debt	$ 1,650.0
Long-term debt (fixed-rate debt), fair value	1,744.6
Term Loan \| Variable-Rate Term Loans
Debt Instrument [Line Items]
Book value of variable rate debt	$ 660.4
Adjustments for ASU 2015-03 \| Long-term Debt
Debt Instrument [Line Items]
Deferred finance costs, net			$ 12.3
Adjustments for ASU 2015-03 \| Other Long-term Assets
Debt Instrument [Line Items]
Deferred finance costs, net			$ (12.3)