Debt - Summary of Long-Term Debt and Related Weighted Average Interest Rates (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-Term Debt	$ 1,973.2	$ 1,718.7
Debt Issuance Costs	(18.4)	(24.2)
Long-Term Debt, Net	1,954.8	1,694.5
Less — Current portion	(23.1)	(240.5)
Long-term debt	1,931.7	1,454.0
Credit Agreement — Term Loan Facility
Debt Instrument [Line Items]
Long-Term Debt	490.6	0.0
Debt Issuance Costs	(2.2)	(2.7)
Long-Term Debt, Net	$ 488.4	$ (2.7)
Weighted Average Interest Rate	1.78%
8.125% Senior Notes due 2020
Debt Instrument [Line Items]
Stated interest rate	8.125%	8.125%
Long-Term Debt	$ 0.0	$ 243.7
Debt Issuance Costs	0.0	(3.2)
Long-Term Debt, Net	$ 0.0	$ 240.5
Weighted Average Interest Rate		8.25%
4.75% Senior Notes due 2023
Debt Instrument [Line Items]
Stated interest rate	4.75%	4.75%
Long-Term Debt	$ 500.0	$ 500.0
Debt Issuance Costs	(5.5)	(6.4)
Long-Term Debt, Net	$ 494.5	$ 493.6
Weighted Average Interest Rate	4.75%	4.75%
5.375% Senior Notes due 2024
Debt Instrument [Line Items]
Stated interest rate	5.375%	5.375%
Long-Term Debt	$ 325.0	$ 325.0
Debt Issuance Costs	(3.2)	(3.6)
Long-Term Debt, Net	$ 321.8	$ 321.4
Weighted Average Interest Rate	5.375%	5.375%
5.25% Senior Notes due 2025
Debt Instrument [Line Items]
Stated interest rate	5.25%	5.25%
Long-Term Debt	$ 650.0	$ 650.0
Debt Issuance Costs	(7.5)	(8.3)
Long-Term Debt, Net	$ 642.5	$ 641.7
Weighted Average Interest Rate	5.25%	5.25%
Other
Debt Instrument [Line Items]
Long-Term Debt	$ 7.6	$ 0.0
Debt Issuance Costs	0.0	0.0
Long-Term Debt, Net	$ 7.6	$ 0.0

Long-term Debt and Capital Lease Obligations, Gross

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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

+ References

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- Definition

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+ References

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- Definition

Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 6
-Section H

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Amount of long-term debt and capital leases due within one year or the normal operating cycle, if longer.

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Amount of long-term debt and capital lease obligations including current maturities.

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- Definition

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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