Unrecognized tax benefits (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax [Abstract]
Balance at Beginning of Year	$ 18.4us-gaap_UnrecognizedTaxBenefits	$ 17.5us-gaap_UnrecognizedTaxBenefits	$ 86.9us-gaap_UnrecognizedTaxBenefits
Tax Positions Related to Prior Years - Additions	1.7	5.7	13.3
Tax Positions Related to Prior Years - Subtractions	0	0	(0.6)
Settlements with Tax Authorities	(0.6)	(4.8)	(23.5)
Lapses of Statute of Limitations	0	0	(61.1)
Tax Positions Taken During Current Year	0.3	0	2.5
Balance at End of Year	19.8us-gaap_UnrecognizedTaxBenefits	18.4us-gaap_UnrecognizedTaxBenefits	17.5us-gaap_UnrecognizedTaxBenefits
Less Tax Attributable to Temporary Items Included Above	(10.4)	(10.2)	(15.0)
Total Unrecognized Tax Benefits that if Recognized Would Affect the Effective Tax Rate	$ 9.4	$ 8.2	$ 2.5

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Unrecognized Tax Benefits Increases (Decreases) Resulting From Other Deductions

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- Definition

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

+ References

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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-Publisher FASB

-Name Accounting Standards Codification

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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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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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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