Goodwill and other intangible assets (Details 1) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Other intangible assets
Finite-Lived Intangible Assets, Gross	$ 2,119.7	$ 2,108.6
Finite-Lived Intangible Assets, Accumulated Amortization	(463.5)	(383.6)
Total other intangible assets	1,656.2	1,725.0
PBM [Member] | Customer Contracts [Member]
Other intangible assets
Finite-Lived Intangible Assets, Gross	2,018.9	2,018.7
Finite-Lived Intangible Assets, Accumulated Amortization	(420.7)	(346.4)
Finite-Lived Intangible Assets, Net	1,598.2	1,672.3
EM [Member] | Customer Relationships [Member]
Other intangible assets
Finite-Lived Intangible Assets, Gross	68.4	68.4
Finite-Lived Intangible Assets, Accumulated Amortization	(35.4)	(32.2)
Finite-Lived Intangible Assets, Net	33.0	36.2
PBM [Member] | Other Intangible Assets [Member]
Other intangible assets
Finite-Lived Intangible Assets, Gross	31.7	20.8
Finite-Lived Intangible Assets, Accumulated Amortization	(7.4)	(5.0)
Finite-Lived Intangible Assets, Net	24.3	15.8
EM [Member] | Other Intangible Assets [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
PBM [Member]
Other intangible assets
Finite-Lived Intangible Assets, Gross	2,050.6	2,039.5
Finite-Lived Intangible Assets, Accumulated Amortization	(428.1)	(351.4)
Finite-Lived Intangible Assets, Net	1,622.5	1,688.1
EM [Member]
Other intangible assets
Finite-Lived Intangible Assets, Gross	69.1	69.1
Finite-Lived Intangible Assets, Accumulated Amortization	(35.4)	(32.2)
Finite-Lived Intangible Assets, Net	$ 33.7	$ 36.9