Goodwill and other intangible assets (Details Textuals) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Goodwill and other intangible assets (Textuals)
Amortization expense of other intangible assets	$ 40.1	$ 40.0	$ 79.8	$ 80.0
Future aggregate amount of amortization expense in 2011			160.3
Future aggregate amount of amortization expense in 2012			160.3
Future aggregate amount of amortization expense in 2013			159.1
Future aggregate amount of amortization expense in 2014			153.5
Future aggregate amount of amortization expense in 2015			135.3
Weighted-average amortization period of intangible assets subject to amortization			15
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Major intangible class, minimum			5
Major intangible class, maximum			20
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Major intangible class, minimum			3
Major intangible class, maximum			10
Amortization of Intangibles, Nonproduction [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization for customer contracts included as an offset to revenues	$ 28.5	$ 28.5	$ 57.0	$ 57.0