Goodwill and other intangibles (Details 1) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Other intangible assets
Finite-Lived Intangible Assets, Gross	$ 2,214.2	$ 2,108.6
Finite-Lived intangible assets, accumulated amortization	593.3	383.6
Total other intangible assets	1,620.9	1,725.0
PBM [Member]
Other intangible assets
Finite-Lived Intangible Assets, Gross	2,145.1	2,039.5
Finite-Lived intangible assets, accumulated amortization	554.8	351.4
Finite-Lived Intangible Assets, Net	1,590.3	1,688.1
EM [Member]
Other intangible assets
Finite-Lived Intangible Assets, Gross	69.1	69.1
Finite-Lived intangible assets, accumulated amortization	38.5	32.2
Finite-Lived Intangible Assets, Net	30.6	36.9
Customer Contracts [Member] | PBM [Member]
Other intangible assets
Finite-Lived Intangible Assets, Gross	2,018.5	2,018.7
Finite-Lived intangible assets, accumulated amortization	494.7	346.4
Finite-Lived Intangible Assets, Net	1,523.8	1,672.3
Customer Relationships [Member] | EM [Member]
Other intangible assets
Finite-Lived Intangible Assets, Gross	68.4	68.4
Finite-Lived intangible assets, accumulated amortization	38.5	32.2
Finite-Lived Intangible Assets, Net	29.9	36.2
Other Intangible Assets [Member] | PBM [Member]
Other intangible assets
Finite-Lived Intangible Assets, Gross	126.6	20.8
Finite-Lived intangible assets, accumulated amortization	60.1	5.0
Finite-Lived Intangible Assets, Net	66.5	15.8
Other Intangible Assets [Member] | EM [Member]
Other intangible assets
Finite-Lived Intangible Assets, Gross	0.7	0.7
Finite-Lived intangible assets, accumulated amortization	0	0
Finite-Lived Intangible Assets, Net	$ 0.7	$ 0.7