Condensed consolidating financial information (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Condensed Consolidating Statement of Cash Flows
Net cash flows provided by (used in) operating activities	$ 2,192.0	$ 2,117.4	$ 1,771.5
Cash flows from investing activities:
Acquisitions, net of cash acquired			(4,672.6)
Purchases of property and equipment	(144.4)	(119.9)	(147.5)
Purchase of short-term investments	(25.0)	(38.0)	(1,201.4)
Sale of short-term investments			1,198.9
Other	0.5	1.7	(4.3)
Net cash used in investing activities - continuing operations	(123.9)	(145.1)	(4,820.5)
Net cash used in investing activities - discontinued operations		(0.8)	(1.9)
Net cash (used in) provided by investing activities	(123.9)	(145.9)	(4,822.4)
Cash flows from financing activities:
Repayment of long-term debt	(0.1)	(1,340.1)	(420.1)
Treasury stock acquired	(2,515.7)	(1,276.2)
Net proceeds from stock issuance			1,569.1
Proceeds from long-term debt, net of discounts	5,580.3		2,491.6
Tax benefit relating to employee stock-based compensation	28.3	58.9	13.4
Other	(2.9)	3.0
Deferred financing fees	(91.6)	(3.9)	(79.5)
Net proceeds from employee stock plans	32.2	35.3	12.5
Net cash provided by (used in) financing activities	3,030.5	(2,523.0)	3,587.0
Effect of foreign currency translation adjustment	(2.2)	4.8	3.6
Net increase (decrease) in cash and cash equivalents	5,096.4	(546.7)	539.7
Cash and cash equivalents at beginning of year	523.7	1,070.4	530.7
Cash and cash equivalents at end of year	5,620.1	523.7	1,070.4
Express Scripts, Inc. [Member]
Condensed Consolidating Statement of Cash Flows
Net cash flows provided by (used in) operating activities	1,846.9	1,709.3	1,684.9
Cash flows from investing activities:
Acquisitions, net of cash acquired			(8,881.7)
Purchases of property and equipment	(124.9)	(53.1)	(116.6)
Purchase of short-term investments			(1,201.4)
Sale of short-term investments			1,198.9
Other	1.0	17.6	6.4
Net cash used in investing activities - continuing operations		(35.5)	8,994.4
Net cash (used in) provided by investing activities	(125.9)	(35.5)	(8,994.4)
Cash flows from financing activities:
Repayment of long-term debt	(0.1)	(1,340.1)	(420.1)
Treasury stock acquired	(2,515.7)	(1,276.2)
Net proceeds from stock issuance			1,569.1
Proceeds from long-term debt, net of discounts	1,494.0		2,491.6
Tax benefit relating to employee stock-based compensation	28.3	58.9	13.4
Other	(2.9)	3.0
Deferred financing fees	(62.4)	(3.9)	(79.5)
Net proceeds from employee stock plans	32.2	35.3	12.5
Net transactions with parent	4,371.1	300.9	4,239.4
Net cash provided by (used in) financing activities	3,344.5	(2,222.1)	7,826.4
Net increase (decrease) in cash and cash equivalents	5,065.5	(548.3)	516.9
Cash and cash equivalents at beginning of year	456.7	1,005.0	488.1
Cash and cash equivalents at end of year	5,522.2	456.7	1,005.0
Aristotle Holding, Inc. [Member]
Condensed Consolidating Statement of Cash Flows
Net cash flows provided by (used in) operating activities	(14.1)
Cash flows from financing activities:
Treasury stock acquired	0
Proceeds from long-term debt, net of discounts	4,086.3
Deferred financing fees	29.2
Net transactions with parent	(4,043.0)
Net cash provided by (used in) financing activities	14.1
Cash and cash equivalents at beginning of year	0
Cash and cash equivalents at end of year	0
Guarantors [Member]
Condensed Consolidating Statement of Cash Flows
Net cash flows provided by (used in) operating activities	753.1	773.2	385.2
Cash flows from investing activities:
Acquisitions, net of cash acquired			(465.9)
Purchases of property and equipment	(13.4)	(61.3)	(22.6)
Other	1.3	(4.3)	(2.7)
Net cash used in investing activities - continuing operations		(65.6)	491.2
Net cash (used in) provided by investing activities	(12.1)	(65.6)	(491.2)
Cash flows from financing activities:
Net transactions with parent	(744.6)	(708.6)	107.1
Net cash provided by (used in) financing activities	(744.6)	(708.6)	107.1
Net increase (decrease) in cash and cash equivalents	(3.6)	(1.0)	1.1
Cash and cash equivalents at beginning of year	9.0	10.0	8.9
Cash and cash equivalents at end of year	5.4	9.0	10.0
Non-Guarantors [Member]
Condensed Consolidating Statement of Cash Flows
Net cash flows provided by (used in) operating activities	26.6	16.8	13.6
Cash flows from investing activities:
Purchases of property and equipment	(6.1)	(5.5)	(8.3)
Purchase of short-term investments		(38.0)
Other	20.2	(0.5)	(1.6)
Net cash used in investing activities - continuing operations		(44.0)	9.9
Net cash used in investing activities - discontinued operations		(0.8)	(1.9)
Net cash (used in) provided by investing activities	14.1	(44.8)	(11.8)
Cash flows from financing activities:
Net transactions with parent	(4.0)	25.8	16.3
Net cash provided by (used in) financing activities	(4.0)	25.8	16.3
Effect of foreign currency translation adjustment	(2.2)	4.8	3.6
Net increase (decrease) in cash and cash equivalents	34.5	2.6	21.7
Cash and cash equivalents at beginning of year	58.0	55.4	33.7
Cash and cash equivalents at end of year	92.5	58.0	55.4
Eliminations [Member]
Condensed Consolidating Statement of Cash Flows
Net cash flows provided by (used in) operating activities	420.5	(381.9)	(312.2)
Cash flows from investing activities:
Acquisitions, net of cash acquired			4,675.0
Net cash used in investing activities - continuing operations			4,675.0
Net cash (used in) provided by investing activities			4,675.0
Cash flows from financing activities:
Net transactions with parent	420.5	381.9	(4,362.8)
Net cash provided by (used in) financing activities	420.5	381.9	(4,362.8)
Cash and cash equivalents at beginning of year	0
Cash and cash equivalents at end of year	$ 0	$ 0