Income Taxes - Roll-Forward of Unrecognized Tax Benefits and Associated Accrued Interest and Penalties (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
Opening balance at January 1	$ 13.0us-gaap_UnrecognizedTaxBenefits	$ 12.8us-gaap_UnrecognizedTaxBenefits	$ 12.6us-gaap_UnrecognizedTaxBenefits
Reductions for tax positions of prior periods	(4.0)
Additions for tax positions of prior periods	0.1	0.8	0.2
Additions related to tax positions taken in the current period	0.2		0.2
Reductions due to lapsed statutes of limitations	(3.1)	(0.6)	(0.2)
Closing balance at December 31	6.2us-gaap_UnrecognizedTaxBenefits	13.0us-gaap_UnrecognizedTaxBenefits	12.8us-gaap_UnrecognizedTaxBenefits
Current	0	(6.8)	(3.0)
Non-current	6.2	6.2	9.8
Interest and Penalties [Member]
Income Tax Contingency [Line Items]
Opening balance at January 1	1.1	0.6	0.4
Reductions for tax positions of prior periods	(0.4)
Additions for tax positions of prior periods	0	0.6	0.2
Additions related to tax positions taken in the current period	0		0
Reductions due to lapsed statutes of limitations	(0.2)	(0.1)	0
Closing balance at December 31	0.5	1.1	0.6
Current	0	(0.6)	(0.3)
Non-current	0.5	0.5	0.3
Unrecognized Tax Benefits [Member]
Income Tax Contingency [Line Items]
Opening balance at January 1	11.9	12.2	12.2
Reductions for tax positions of prior periods	(3.6)
Additions for tax positions of prior periods	0.1	0.2	0
Additions related to tax positions taken in the current period	0.2		0.2
Reductions due to lapsed statutes of limitations	(2.9)	(0.5)	(0.2)
Closing balance at December 31	5.7	11.9	12.2
Current	0	(6.2)	(2.7)
Non-current	$ 5.7	$ 5.7	$ 9.5

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The current portion of the amount recognized for uncertain tax positions as of the balance sheet date.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.20)

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The noncurrent portion of the amount recognized for uncertain tax positions as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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