Debt - Schedule of Long-Term Debt Instruments (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total short-term debt	$ 92.0	$ 80.0
Long-term debt, net	2,156.4	2,145.3
Debt issuance costs	(23.6)	(24.7)
Total debt, net	$ 2,248.4	$ 2,225.3
Weighted average cost of debt	4.90%	4.80%
Secured debt \| Term loan, due 2024
Debt Instrument [Line Items]
Long-term debt, net	$ 667.9	$ 667.8
Maturity date	Mar. 16, 2024	Mar. 16, 2024
Senior unsecured notes
Debt Instrument [Line Items]
Long-term debt, net	$ 1,502.1	$ 1,502.2
Senior unsecured notes \| 5.250% senior unsecured notes, due 2022
Debt Instrument [Line Items]
Long-term debt, net	$ 549.6	$ 549.6
Stated interest rate	5.25%	5.25%
Maturity date	Jan. 31, 2022	Jan. 31, 2022
Senior unsecured notes \| 5.625% senior unsecured notes, due 2024
Debt Instrument [Line Items]
Long-term debt, net	$ 502.5	$ 502.6
Stated interest rate	5.625%	5.625%
Maturity date	Jan. 31, 2024	Jan. 31, 2024
Senior unsecured notes \| 5.875% senior unsecured notes, due 2025
Debt Instrument [Line Items]
Long-term debt, net	$ 450.0	$ 450.0
Stated interest rate	5.875%	5.875%
Maturity date	Mar. 15, 2025	Mar. 15, 2025
Short-term debt \| AR Facility
Debt Instrument [Line Items]
Credit facility, outstanding amount	$ 92.0	$ 80.0
Long-term debt \| Revolving credit facility
Debt Instrument [Line Items]
Credit facility, outstanding amount	$ 10.0	$ 0.0

Contractual interest rate for funds borrowed, under the debt agreement.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Represents the aggregate of total long-term debt, including current maturities and short-term debt.

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Weighted average interest rate of debt outstanding.

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- Definition

Fair value of the amount outstanding under the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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