Income taxes - Income and Taxes from Cont. Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Income (loss) from continuing operations before income taxes [Abstract]
Income from continuing operations before tax	$ 10.7	$ 44.3
Income tax expense (benefit) from continuing operations [Abstract]
Deferred income taxes	(12.8)	(26.4)
Provision (benefit) for income taxes	4.9	16.6
Comprehensive provision (benefit) for income taxes allocation [Abstract]
Discontinued operations	0.1	(0.3)
Other comprehensive income (loss)	$ (6.5)	$ (5.9)

The component of income tax expense for the period representing the increase (decrease) in the entity's deferred tax assets and liabilities pertaining to continuing operations.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 109

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Deferred Tax Expense (or Benefit)

-URI http://asc.fasb.org/extlink&oid=6510177

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-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph h

-Article 4

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-Name Accounting Standards Codification

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Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section I

-Subsection 7

+ Details

- Definition

Tax effect allocated to a disposal group that is classified as a component of the entity reported as a separate component of income before extraordinary items. Includes the tax effects of the following: income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

+ References

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to continuing operations.

+ References+ Details

- Definition

Tax effect of other comprehensive income (loss) attributable to both parent entity and noncontrolling interest.

+ References

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-Name Accounting Research Bulletin (ARB)

-Number 51

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+ Details