Summary of significant accounting policies (Details Textuals) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2010 Year Day Subsidiary	Dec. 31, 2009	Dec. 31, 2008
Summary of significant accounting policies (Textuals) [Abstract]
Original maturities of cash on hand and investment	3 months or less
Negative book balances carried by cash disbursement accounts	$ 418.8	$ 330.8
Restricted cash and investments	16.3	9.1
Unbilled receivables for continuing operations	911.3	1,218.4
Typical period for billing of unbilled receivable	30
Allowance for doubtful accounts for continuing operations	64.8	93.4
Percentage of allowance for doubtful accounts for continuing operations	3.80%	3.70%
Trading securities, included in other assets	13.5	11.4
Net gain (loss) recognized on the trading portfolio	1.5	3.8	(5.2)
Retail pharmacy co-payments included in Network revenues	6,181.4	3,132.1	3,153.6
Vesting period of stock option plan	3
Cumulative translation adjustments, credit balances	19.8	14.1
Foreign currency translation adjustments	$ 5.7	$ 7.9	$ (14.7)
Recorded percentage of the assets and liabilities at fair value, including goodwill (in percentage)	100.00%
Minimum percentage of ownership in affiliates for accounting under equity method of accounting	20.00%
Maximum percentage of ownership in affiliates for accounting under equity method of accounting	50.00%
Internally Developed Software [Member]
Other Intangible Assets [Line Items]
Maximum estimated economic life of internally developed software (in years)	5
First one-third of Grants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of compensation costs recognition for grants that vest over three years	12
Second one-third of Grants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of compensation costs recognition for grants that vest over three years	24
Third one-third of Grants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of compensation costs recognition for grants that vest over three years	36

Capitalized Computer Software Amortization Period Maximum.

Name:	esrx_CapitalizedComputerSoftwareAmortizationPeriodMaximum
Namespace Prefix:	esrx
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

Negative book balances carried by cash disbursement accounts.

+ Details

Name:	esrx_CashAndCashEquivalentsNegativeBookBalancesCarriedByCashDisbursementAccounts
Namespace Prefix:	esrx
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum percentage of ownership in affiliates for accounting under equity method of accounting.

+ Details

Name:	esrx_MaximumPercentageOfOwnershipInAffiliatesForAccountingUnderEquityMethodOfAccounting
Namespace Prefix:	esrx
Data Type:	us-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum period for billing of unbilled receivable

+ Details

Name:	esrx_MaximumPeriodForBillingOfUnbilledReceivable
Namespace Prefix:	esrx
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum percentage of ownership in affiliates for accounting under equity method of accounting.

+ Details

Name:	esrx_MinimumPercentageOfOwnershipInAffiliatesForAccountingUnderEquityMethodOfAccounting
Namespace Prefix:	esrx
Data Type:	us-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Original maturities of cash on hand and investment.

+ Details

Name:	esrx_OriginalMaturitiesOfCashOnHandAndInvestment
Namespace Prefix:	esrx
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Allowance for doubtful accounts receivable.

+ Details

Name:	esrx_PercentageOfAllowanceForDoubtfulAccountsReceivable
Namespace Prefix:	esrx
Data Type:	us-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of compensation costs recognition for grants that vest over three years.

+ Details

Name:	esrx_PeriodOfCompensationCostsRecognitionForGrantsThatVestOverThreeYears
Namespace Prefix:	esrx
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Retail Pharmacy Co Payments Included In Network Revenues.

+ Details

Name:	esrx_RetailPharmacyCoPaymentsIncludedInNetworkRevenues
Namespace Prefix:	esrx
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Summary of significant accounting policies.

+ Details

Name:	esrx_SummaryOfSignificantAccountingPoliciesTextualsAbstract
Namespace Prefix:	esrx
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains (losses).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 52

-Paragraph 12, 13

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 52

-Paragraph 31

-Subparagraph a

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 12

-Paragraph 10

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

-Paragraph 17, 18, 19, 22, 23, 24, 25, 26

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 45

+ Details

Name:	us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 4

-Article 5

+ Details

Name:	us-gaap_AllowanceForDoubtfulAccountsReceivable
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of purchase price allocated to assets and liabilities acquired at their respective fair values.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 88-16

+ Details

Name:	us-gaap_LeveragedBuyoutPercentageOfPurchasePriceAllocatedToAssetsAndLiabilitiesAcquiredAtFairValue
Namespace Prefix:	us-gaap
Data Type:	us-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Adjustment that results from the process of translating subsidiary financial statements and foreign equity investments into functional currency of the reporting entity, net of tax.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 52

-Paragraph 13, 20, 31

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 38

-Subparagraph c(3)

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

-Paragraph 24

-Subparagraph b

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

-Paragraph 14, 17, 19, 26

+ Details

Name:	us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPeriodIncreaseDecrease
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

The current cash, cash equivalents and investments that are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. Includes current cash equivalents and investments that are similarly restricted as to withdrawal, usage or disposal.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5

+ Details

Name:	us-gaap_RestrictedCashAndInvestmentsCurrent
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Description of the period of time over which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, which may be expressed in a variety of ways (for example, in years, month and year).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph a

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod
Namespace Prefix:	us-gaap
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total of financial instruments that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time, usually less than one year or the normal operating cycle, whichever is longer) or for debt and equity securities formerly categorized as available-for-sale or held-to-maturity which the entity held as of the date it opted to account for such securities at fair value. An enterprise may also categorize such a security as trading without the intent to sell it in the near term assuming the decision to categorize the security as trading occurred at acquisition; this is the reason why the trading category of investments in debt and equity securities are bought and sold "principally" for sale in the near term. Transfers into and out of the trading category should be rare. Such financial instruments that are held as of the reporting date are measured at fair value with unrealized holding gains and losses (the difference between fair value and the previously reported carrying amount) included in earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 159

-Paragraph 29

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Implementation Guide (Q and A)

-Number FAS115

-Paragraph 35

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph a

+ Details

Name:	us-gaap_TradingSecuritiesCurrent
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

For trading securities held as of the balance sheet date, this amount represents the difference between the fair value of trading securities and their carrying value (unrealized holding gain or loss). Trading securities are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) and such unrealized holding gain or loss is included in earnings for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph a

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 21

-Subparagraph e

+ Details

Name:	us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Unbilled amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the entity and, at a minimum, one other party. An example would be amounts associated with contracts or programs where the recognized revenue for performance thereunder exceeds the amounts billed under the terms thereof as of the date of the balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Subparagraph c(3)

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 43

-Chapter 11

-Section A

-Paragraph 4, 21

+ Details

Name:	us-gaap_UnbilledContractsReceivable
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant