Condensed consolidating financial information (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Condensed Consolidating Statement of Operations
Revenues	$ 12,101.4	$ 11,571.0	$ 11,361.4	$ 11,094.5	$ 11,294.2	$ 11,251.8	$ 11,288.8	$ 11,138.4	$ 46,128.3	[1]	$ 44,973.2	[1]	$ 24,722.3	[1]
Operating expenses									43,816.6		42,902.3		23,224.8
Operating income	574.9	605.1	579.3	552.4	557.9	528.0	530.3	454.7	2,311.7		2,070.9		1,497.5
Interest (expense) income, net									(287.3)		(162.2)		(189.1)
Income before income taxes									2,024.4		1,908.7		1,308.4
Provision for income taxes									748.6		704.1		481.8
Net income from continuing operations					329.6	307.1	307.3	260.6	1,275.8		1,204.6		826.6
Net (loss) income from discontinued operations, net of tax						(5.6)	(17.4)	(0.4)	0		(23.4)		1.0
Net income (loss)	290.4	324.7	334.2	326.5	329.6	301.5	289.9	260.2	1,275.8		1,181.2		827.6
Express Scripts, Inc. [Member]
Condensed Consolidating Statement of Operations
Revenues									29,450.9		29,594.6		14,642.9
Operating expenses									27,847.9		28,176.8		13,654.9
Operating income									1,603.0		1,417.8		988.0
Interest (expense) income, net									(259.8)		(156.2)		(179.6)
Income before income taxes									1,343.2		1,261.6		808.4
Provision for income taxes									487.9		462.3		293.0
Net income from continuing operations									855.3		799.3		515.4
Equity in earnings of subsidiaries									420.5		381.9		312.2
Net income (loss)									1,275.8		1,181.2		827.6
Aristotle Holding, Inc. [Member]
Condensed Consolidating Statement of Operations
Interest (expense) income, net									(22.2)
Income before income taxes									(22.2)
Provision for income taxes									(8.1)
Net income from continuing operations									(14.1)
Net income (loss)									(14.1)
Guarantors [Member]
Condensed Consolidating Statement of Operations
Revenues									16,520.3		15,287.8		10,004.2
Operating expenses									15,841.3		14,635.8		9,497.7
Operating income									679.0		652.0		506.5
Interest (expense) income, net									(5.9)		(6.2)		(6.5)
Income before income taxes									673.1		645.8		500.0
Provision for income taxes									263.8		241.0		185.9
Net income from continuing operations									409.3		404.8		314.1
Net income (loss)									409.3		404.8		314.1
Non-Guarantors [Member]
Condensed Consolidating Statement of Operations
Revenues									157.1		90.8		75.2
Operating expenses									127.4		89.7		72.2
Operating income									29.7		1.1		3.0
Interest (expense) income, net									0.6		0.2		(3.0)
Income before income taxes									30.3		1.3
Provision for income taxes									5.0		0.8		2.9
Net income from continuing operations									25.3		0.5		(2.9)
Net (loss) income from discontinued operations, net of tax											(23.4)		1.0
Net income (loss)									25.3		(22.9)		(1.9)
Eliminations [Member]
Condensed Consolidating Statement of Operations
Equity in earnings of subsidiaries									420.5		(381.9)		(312.2)
Net income (loss)									$ 420.5		$ (381.9)		$ (312.2)

[1] Includes retail pharmacy co-payments of $5786.6, $6,181.4, and $3,132.1, for the years ended December 31, 2011, 2010, and 2009, respectively.