Accelerated Share Repurchase, shares to be received from investment bank. Accelerated Share Repurchase Shares To Be Received From Investment Bank Accelerated Share Repurchase, shares to be received from investment bank Accelerated share repurchases settlement number of shares received. Accelerated Share Repurchases Settlement Number Of Shares Received [Member] ASR Agreement 2 [Member] Accelerated Share Repurchases Settlement Payment Or Receipt Settled portion of total agreement Accounts Payable Current Accounts payable Accounts receivable financing facility. Accounts Receivable Financing Facility [Member] Accounts Receivable Financing Facility [Member] Accounts Receivable Net Accounts receivables Accrued Liabilities Current Accrued expenses Accumulated Amortization Accumulated Amortization Accumulated amortization Accumulated amortization goodwill. Accumulated Amortization Goodwill Accumulated Amortization Accumulated Amortization Intangible Assets Total Accumulated Amortization Intangible Assets Total Accumulated amortization Accumulated Depreciation Depletion And Amortization Property Plant And Equipment Less accumulated depreciation Accumulated Other Comprehensive Income Loss Net Of Tax Accumulated other comprehensive income Accumulated Other Comprehensive Income [Member] Accumulated Other Comprehensive Income [Member] Acquired Finite Lived Intangible Asset Amount Excess amount of purchase price over tangible net assets allocated to intangible assets Acquired Finite Lived Intangible Assets Weighted Average Useful Life Estimated useful life of allocated intangible assets Additional Cash And Cash Equivalent Related Text Average maturity period of investment in AAA-rated money market mutual funds, days Additional Paid In Capital Common Stock Additional paid-in capital Additional Paid In Capital [Member] Additional Paid-In Capital [Member] Adjusted Net Income Adjusted Net Income Adjusted net income Adjusted Retained Earnings Adjusted Retained Earnings Retroactive earnings Adjustments Noncash Items To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities Non-cash adjustments to net income Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustment To Prior Period Resulting In Increase In Cash Provided By Operating Activities Adjustment To Prior Period Resulting In Increase In Cash Provided By Operating Activities Increase in cash flows from operating activities Allocated Share Based Compensation Expense Recognized stock-based compensation expense Amendment Flag Amendment Flag Amortization Of Financing Costs Deferred financing fees Amortization Of Intangible Assets Amortization expense of other intangible assets Amounts Recognized As Of Acquisition Date As Adjusted [Member] Amounts Recognized As Of Acquisition Date As Adjusted [Member] Amounts Recognized As Of Acquisition Date [Member] Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount Antidilutive shares excluded from basic and diluted EPS calculations Aristotle Holding [Member] Aristotle Holding [Member] Aristotle Holding, Inc.[Member] Assets Total assets Total assets Assets [Abstract] Assets Assets Current Total current assets Assets Current [Abstract] Current assets: Assets Held For Sale Long Lived Total assets Assets Held For Sale Property Plant And Equipment Property and equipment Award Type [Axis] Award Type [Axis] Bridge facility. Bridge Facility [Member] Bridge Facility [Member] Business Acquisition Acquiree [Domain] Business Acquisition, Acquiree [Domain] Business Acquisition [Axis] Business Acquisition Business Acquisition Cost Of Acquired Entity Cash Paid Cash paid to Medco stockholders Business Acquisition Cost Of Acquired Entity Equity Interests Issued And Issuable Value of shares issued to Medco Value of stock options and restricted shares issued to Medco holders Business Acquisition Equity Interest Issued Or Issuable Basis For Determining Value Basis For Determining Value, description Business acquisition equity interest issued or issuable basis for determining value acquirer opening share price. Business Acquisition Equity Interest Issued Or Issuable Basis For Determining Value Acquirer Opening Share Price Basis for determining value, Express Scripts opening share price Business Acquisition Equity Interest Issued Or Issuable Description Total consideration description, equity interest issued or Issuable Business Acquisition [Line Items] Business Acquisition [Line Items] Business Acquisition Net Cash Paid For Entity Business Acquisition Net Cash Paid For Entity Acquisitions, net of cash acquired Business Acquisition Percentage Of Voting Interests Acquired Percentage of voting rights company owned Business Acquisition Pro Forma Earnings Per Share Basic Basic earnings per share Business Acquisition Pro Forma Earnings Per Share Diluted Diluted earnings per share Business Acquisition Pro Forma Information [Text Block] Summary of Combined Results of Operations Business acquisition purchase consideration payable in cash per share. Business Acquisition Purchase Consideration Payable In Cash Per Share Cash paid per share for shareholders Business acquisition purchase consideration replacement award exchange ratio. Business Acquisition Purchase Consideration Replacement Award Exchange Ratio Replacement awards exchange ratio Business acquisition purchase consideration replacement award shares exchange ratio. Business Acquisition Purchase Consideration Replacement Award Shares Exchange Ratio Stock paid per share ratio for shareholders Business Acquisition Purchase Price Allocation Assets Acquired Liabilities Assumed Net Total Business Acquisition Purchase Price Allocation Current Assets Current assets Business Acquisition Purchase Price Allocation Deferred Tax Liabilities Noncurrent Deferred income taxes Business Acquisition Purchase Price Allocation Goodwill Amount Excess amount of purchase price over tangible net assets allocated to goodwill Goodwill Business Acquisition Purchase Price Allocation Goodwill Expected Tax Deductible Amount Goodwill expected to be deductible for income tax purposes Business Acquisition Purchase Price Allocation Intangible Assets Other Than Goodwill Acquired intangible assets Business Acquisition Purchase Price Allocation Liabilities Assumed Current liabilities Business Acquisition Purchase Price Allocation Noncurrent Liabilities Long Term Debt Long-term debt Business Acquisition Purchase Price Allocation Other Noncurrent Assets Other noncurrent assets Business Acquisition Purchase Price Allocation Other Noncurrent Liabilities Other noncurrent liabilities Business Acquisition Purchase Price Allocation Property Plant And Equipment Property and equipment Business Acquisitions Pro Forma Net Income Loss Net income Business Acquisitions Pro Forma Revenue Total revenues Business Combination Acquired Receivables Estimated Uncollectible Accounts receivable balances, acquired and estimated as uncollectible Business Combination Acquired Receivables Fair Value Fair value Business Combination Acquired Receivables Gross Contractual Amount Gross contractual amounts receivable Business Combination Consideration Transferred Total consideration Business Combination Disclosure [Text Block] Changes in business Capitalized Computer Software Additions Capitalized amount of internally developed software Capitalized Computer Software Net Net of accumulated depreciation of internally developed software Carrying amount of the swaps and bank fees. Carrying Amount Of Swaps And Bank Fees Carrying amount of the swaps and bank fees Cash And Cash Equivalents At Carrying Value Cash and cash equivalents at end of period Cash and cash equivalents at beginning of period Cash and cash equivalents Cash And Cash Equivalents Fair Value Disclosure Cash equivalents Cash And Cash Equivalents Period Increase Decrease Net (decrease) increase in cash and cash equivalents Net (decrease) increase in cash and cash equivalents Cash Flows Statement Data [Text Block] Cash Flows Statement Data [Text Block] Revision of Condensed Consolidating Statement of Cash Flows Cash Provided By Used In Investing Activities Discontinued Operations Net cash used in investing activities - discontinued operations Claims and rebates payable. Claims And Rebates Payable Claims and rebates payable Classification Adjustment To Prior Period Resulting In Increase In Investing Activities And Decrease In Financing Activities Classification Adjustment To Prior Period Resulting In Increase In Investing Activities And Decrease In Financing Activities Decrease in cash flows from financing activities Class Of Stock [Domain] Class of Stock [Domain] Class Of Treasury Stock [Table] Class of Treasury Stock [Table] Client accounts receivables. Client Accounts Receivables [Member] Client Accounts Receivables [Member] Commitments And Contingencies Commitments and contingencies (Note 13) Commitments And Contingencies Disclosure [Line Items] Commitments And Contingencies Disclosure [Line Items] Commitments And Contingencies Disclosure [Line Items] Commitments And Contingencies Disclosure [Table] Commitments And Contingencies Disclosure [Table] Commitments And Contingencies Disclosure [Table] Commitments And Contingencies Disclosure [Text Block] Commitments and contingencies Commitments [Line Items] Commitments [Line Items] Commitments [Line Items] Commitments [Table] Commitments [Table] Commitments [Table] Common Stock [Member] Common Stock [Member] Common Stock Par Or Stated Value Per Share Common stock, par value per share Common Stock Shares Authorized Common stock, shares authorized Common Stock Shares Issued Common stock, shares issued Common Stock Shares Outstanding Common stock, shares outstanding Common stock under accelerated share repurchase agreement. Common Stock Under Accelerated Share Repurchase Agreement [Member] Common Stock Under Accelerated Share Repurchase Agreement [Member] Common Stock Value Common stock, 2,985.0 shares authorized, $0.01 par value per share; shares issued: 809.6 and 690.7, respectively; shares outstanding: 809.6 and 484.6, respectively Comprehensive Income Net Of Tax Comprehensive income Comprehensive income Comprehensive Income Net Of Tax [Abstract] Other comprehensive income (loss), net of tax: Condensed Financial Statements Captions [Line Items] Condensed Financial Statements, Captions [Line Items] Condensed Financial Statements [Text Block] Condensed consolidating financial information ConnectYourCare [Member] Connect Your Care [Member] CYC [Member] Consolidation Eliminations [Member] Eliminations [Member] Contingencies And Commitments [Line Items] Contingencies And Commitments [Line Items] Contingencies And Commitments [Line Items] Contingencies And Commitments [Table] Contingencies And Commitments [Table] Contingencies And Commitments [Table] Cost Of Revenue Cost of revenues Costs And Expenses Operating expenses Cumulative Amortization Of Basis Adjustment Cumulative Amortization Of Basis Adjustment Cumulative adjustment to amortization expense Current Fiscal Year End Date Current Fiscal Year End Date Customer Contracts [Member] Customer Contracts [Member] Customer Relationships [Member] Customer Relationships [Member] Debt Disclosure [Text Block] Financing Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument Basis Spread On Variable Rate Basis points Debt Instrument Face Amount Senior notes aggregate principal amount Debt Instrument Interest Rate Stated Percentage Interest rate on debt instruments Debt Instrument [Line Items] Debt Instrument [Line Items] Debt Instrument Name [Domain] Debt Instrument, Name [Domain] Debt Instrument Repurchased Face Amount Senior Notes principal amount Debt Instrument [Table] Schedule of Long-term Debt Instruments [Table] Debt Longterm And Shortterm Combined Amount [Abstract] Long-term debt: Deferred Tax Assets Net Current Deferred taxes Deferred Tax Liability Not Recognized [Line Items] Deferred Tax Liability Not Recognized [Line Items] Deferred Tax Liability Not Recognized [Table] Deferred Tax Liability Not Recognized [Table] Defined Benefit Plan Benefit Obligation Fair value of the projected benefit obligation Defined Benefit Plan Benefits Paid Pension paid in second quarter Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Defined benefit plan expected additional contributions. Defined Benefit Plan Expected Additional Contributions Expected Additional Contributions Defined Benefit Plan Expected Return On Plan Assets Expected return on plan assets Defined benefit plan expected return rate on plan assets. Defined Benefit Plan Expected Return Rate On Plan Assets Percentage of expected rate of return assumption on pension plan Defined Benefit Plan Fair Value Of Plan Assets Plan assets at fair value total Defined Benefit Plan Funded Status Of Plan Funded status and the balance sheet liability Defined Benefit Plan Interest Cost Interest cost Defined Benefit Plans Disclosures Defined Benefit Plans [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plans [Domain] Defined Benefit Plans and Other Postretirement Benefit Plans [Domain] Defined Benefit Plan Service Cost Service cost Depreciation Depreciation expense Depreciation And Amortization Depreciation and amortization Depreciation and amortization expense Derivative Amount Of Hedged Item Maximum capacity of swap Derivative Average Basis Spread On Variable Rate Weighted average spread Derivative By Nature [Axis] Derivative, by Nature [Axis] Derivative Name [Domain] Derivative, Name [Domain] Disclosure Assets Held For Sale Additional Information [Abstract] Disclosure Assets Held For Sale Additional Information [Abstract] Disclosure Assets Held For Sale Additional Information [Abstract] Disclosure - Changes in business - Additional Information [Abstract] Disclosure Changes In Business Additional Information [Abstract] Disclosure - Changes in business - Additional Information [Abstract] Disclosure - Changes in business - Components of Preliminary Purchase Price Allocation [Abstract] Disclosure Changes In Business Components Of Preliminary Purchase Price Allocation [Abstract] Disclosure - Changes in business - Components of Preliminary Purchase Price Allocation [Abstract] Disclosure - Changes in business - Estimated Bad Debt Related to Manufacturer Accounts Receivables and Client Accounts Receivables [Abstract] Disclosure Changes In Business Estimated Bad Debt Related To Manufacturer Accounts Receivables And Client Accounts Receivables [Abstract] Disclosure - Changes in business - Estimated Bad Debt Related to Manufacturer Accounts Receivables and Client Accounts Receivables [Abstract] Disclosure - Changes in business - Summary of Combined Results of Operations [Abstract] Disclosure Changes In Business Summary Of Combined Results Of Operations [Abstract] Disclosure - Changes in business - Summary of Combined Results of Operations [Abstract] Disclosure - Changes in business - Summary of Purchase Price [Abstract] Disclosure Changes In Business Summary Of Purchase Price [Abstract] Disclosure - Changes in business - Summary of Purchase Price [Abstract] Disclosure Commitments And Contingencies Additional Information [Abstract] Disclosure Commitments And Contingencies Additional Information [Abstract] Disclosure Commitments And Contingencies Additional Information [Abstract] Disclosure - Commitments and contingencies - Future Minimum Lease Payments Due Under Noncancellable Operating Leases [Abstract] Disclosure Commitments And Contingencies Future Minimum Lease Payments Due Under Noncancellable Operating Leases [Abstract] Disclosure - Commitments and contingencies - Future Minimum Lease Payments Due Under Noncancellable Operating Leases [Abstract] Disclosure - Commitments and contingencies - Summary of Future Purchase Commitments [Abstract] Disclosure Commitments And Contingencies Summary Of Future Purchase Commitments [Abstract] Disclosure - Commitments and contingencies - Summary of Future Purchase Commitments [Abstract] Disclosure - Common stock - Additional Information [Abstract] Disclosure Common Stock Additional Information [Abstract] Disclosure - Common stock - Additional Information [Abstract] Disclosure - Condensed consolidating financial information - Additional Information [Abstract] Disclosure Condensed Consolidating Financial Information Additional Information [Abstract] Disclosure - Condensed consolidating financial information - Additional Information [Abstract] Disclosure C O N D E N S E D C O N S O L I D A T I N G F I N A N C I A L I N F O R M A T I O N Condensed Consolidating Balance Sheet [Abstract] Disclosure C O N D E N S E D C O N S O L I D A T I N G F I N A N C I A L I N F O R M A T I O N Condensed Consolidating Balance Sheet [Abstract] Disclosure C O N D E N S E D C O N S O L I D A T I N G F I N A N C I A L I N F O R M A T I O N Condensed Consolidating Balance Sheet [Abstract] Disclosure - Condensed consolidating financial information - Condensed Consolidating Statement of Cash Flows [Abstract] Disclosure Condensed Consolidating Financial Information Condensed Consolidating Statement Of Cash Flows [Abstract] Disclosure - Condensed consolidating financial information - Condensed Consolidating Statement of Cash Flows [Abstract] Disclosure - Condensed consolidating financial information - Condensed Consolidating Statement of Operations [Abstract] Disclosure Condensed Consolidating Financial Information Condensed Consolidating Statement Of Operations [Abstract] Disclosure - Condensed consolidating financial information - Condensed Consolidating Statement of Operations [Abstract] Disclosure - Earnings per share - Schedule of Weighted Average Number of Shares [Abstract] Disclosure Earnings Per Share Schedule Of Weighted Average Number Of Shares [Abstract] Disclosure - Earnings per share - Schedule of Weighted Average Number of Shares [Abstract] Disclosure Fair Value Measurements Additional Information [Abstract] Disclosure Fair Value Measurements Additional Information [Abstract] Disclosure Fair Value Measurements Additional Information [Abstract] Disclosure - Fair value measurements - Carrying Values and Fair Values of Senior Notes [Abstract] Disclosure Fair Value Measurements Carrying Values And Fair Values Of Senior Notes [Abstract] Disclosure - Fair value measurements - Carrying Values and Fair Values of Senior Notes [Abstract] Disclosure - Financing - Additional Information [Abstract] Disclosure Financing Additional Information [Abstract] Disclosure - Financing - Additional Information [Abstract] Disclosure - Financing - Summary of Company's Debt, Net of Unamortized Discounts [Abstract] Disclosure Financing Summary Of Companys Debt Net Of Unamortized Discounts [Abstract] Disclosure - Financing - Summary of Company's Debt, Net of Unamortized Discounts [Abstract] Disclosure Goodwill And Other Intangible Assets Additional Information [Abstract] Disclosure Goodwill And Other Intangible Assets Additional Information [Abstract] Disclosure Goodwill And Other Intangible Assets Additional Information [Abstract] Disclosure - Goodwill and other intangible assets - Summary of Change in Net Carrying Value of Goodwill by Business Segment [Abstract] Disclosure Goodwill And Other Intangible Assets Summary Of Change In Net Carrying Value Of Goodwill By Business Segment [Abstract] Disclosure - Goodwill and other intangible assets - Summary of Change in Net Carrying Value of Goodwill by Business Segment [Abstract] Disclosure - Goodwill and other intangible assets - Summary of Goodwill and Other Intangible Assets [Abstract] Disclosure Goodwill And Other Intangible Assets Summary Of Goodwill And Other Intangible Assets [Abstract] Disclosure - Goodwill and other intangible assets - Summary of Goodwill and Other Intangible Assets [Abstract] Disclosure Income Taxes Additional Information [Abstract] Disclosure Income Taxes Additional Information [Abstract] Disclosure Income Taxes Additional Information [Abstract] Disclosure - Income taxes - Unrecognized Tax Benefits Roll-Forward [Abstract] Disclosure Income Taxes Unrecognized Tax Benefits Roll Forward [Abstract] Disclosure - Income taxes - Unrecognized Tax Benefits Roll-Forward [Abstract] Disclosure Of Compensation Related Costs Share Based Payments [Text Block] Stock-based compensation plans Disclosure Of Long Lived Assets Held For Sale [Text Block] Dispositions Disclosure - Pension and other post-retirement benefits - Additional Information [Abstract] Disclosure Pension And Other Postretirement Benefits Additional Information [Abstract] Disclosure - Pension and other post-retirement benefits - Additional Information [Abstract] Disclosure - Pension and other post-retirement benefits - Net Pension and Postretirement Benefit Cost [Abstract] Disclosure Pension And Other Postretirement Benefits Net Pension And Postretirement Benefit Cost [Abstract] Disclosure - Pension and other post-retirement benefits - Net Pension and Postretirement Benefit Cost [Abstract] Disclosure P R O P E R T Y A N D E Q U I P M E N T Additional Information [Abstract] Disclosure P R O P E R T Y A N D E Q U I P M E N T Additional Information [Abstract] Disclosure P R O P E R T Y A N D E Q U I P M E N T Additional Information [Abstract] Disclosure - Property and equipment - Property and Equipment, at Cost [Abstract] Disclosure Property And Equipment Property And Equipment At Cost [Abstract] Disclosure - Property and equipment - Property and Equipment, at Cost [Abstract] Disclosure - Revision of Condensed Consolidating Statement of Cash Flows [Abstract] Disclosure Revision Of Condensed Consolidating Statement Of Cash Flows [Abstract] Disclosure - Revision of Condensed Consolidating Statement of Cash Flows [Abstract] Disclosure Segment Information Additional Information [Abstract] Disclosure Segment Information Additional Information [Abstract] Disclosure Segment Information Additional Information [Abstract] Disclosure - Segment information - Reportable Segments Information [Abstract] Disclosure Segment Information Reportable Segments Information [Abstract] Disclosure - Segment information - Reportable Segments Information [Abstract] Disclosure - Segment information - Segments Reporting Information, Assets [Abstract] Disclosure Segment Information Segments Reporting Information Assets [Abstract] Disclosure - Segment information - Segments Reporting Information, Assets [Abstract] Disclosure - Stock-based compensation plans - Activity Related to Non-Vested Options [Abstract] Disclosure Stockbased Compensation Plans Activity Related To Non Vested Options [Abstract] Disclosure - Stock-based compensation plans - Activity Related to Non-Vested Options [Abstract] Disclosure Stock Based Compensation Plans Additional Information [Abstract] Disclosure Stock Based Compensation Plans Additional Information [Abstract] Disclosure Stock Based Compensation Plans Additional Information [Abstract] Disclosure - Stock-based compensation plans - Status of Restricted Stock Units and Performance Shares [Abstract] Disclosure Stockbased Compensation Plans Status Of Restricted Stock Units And Performance Shares [Abstract] Disclosure - Stock-based compensation plans - Status of Restricted Stock Units and Performance Shares [Abstract] Disclosure - Stock-based compensation plans - Status of Stock Options and SSRs [Abstract] Disclosure Stockbased Compensation Plans Status Of Stock Options And S S Rs [Abstract] Disclosure - Stock-based compensation plans - Status of Stock Options and SSRs [Abstract] Disclosure - Stock-based compensation plans - Summarized Information Related to Non-Vested Restricted Stock Units [Abstract] Disclosure Stockbased Compensation Plans Summarized Information Related To Non Vested Restricted Stock Units [Abstract] Disclosure - Stock-based compensation plans - Summarized Information Related to Non-Vested Restricted Stock Units [Abstract] Disclosure - Stock-based compensation plans - Weighted Average Assumptions to Value Options and SSRs Granted [Abstract] Disclosure Stockbased Compensation Plans Weighted Average Assumptions To Value Options And S S Rs Granted [Abstract] Disclosure - Stock-based compensation plans - Weighted Average Assumptions to Value Options and SSRs Granted [Abstract] Disclosure Summary Of Significant Accounting Policies Additional Information [Abstract] Disclosure Summary Of Significant Accounting Policies Additional Information [Abstract] Disclosure Summary Of Significant Accounting Policies Additional Information [Abstract] Discontinued Operations [Table] Discontinued Operations [Table] Discontinued Operations [Table] Disposal Group Not Discontinued Operation Assets Disposal Group Not Discontinued Operation Assets Total assets Disposal Group Not Discontinued Operation Cash And Cash Equivalents Disposal Group Not Discontinued Operation Cash And Cash Equivalents Cash Disposal Group Not Discontinued Operation Gain Loss On Disposal Gain on the sale related to disposal of the business Disposal Group Not Discontinued Operation Gain Loss On Disposal Income Statement Caption Operating income (loss) Disposal Group Not Discontinued Operation Goodwill Disposal Group Not Discontinued Operation Goodwill Goodwill Gross carrying amount, disposition Disposal Group Not Discontinued Operation Goodwill And Intangible Assets Disposal Group Not Discontinued Operation Goodwill And Intangible Assets Gross carrying amount, disposition Disposal Group Not Discontinued Operation Operating Income Loss Disposal Group Not Discontinued Operation Operating Income Loss Operating income (loss) Disposal Group Not Discontinued Operation Restricted Cash Disposal Group Not Discontinued Operation Restricted Cash Restricted cash Disposal Groups Including Discontinued Operations Name [Domain] Disposal Groups, Including Discontinued Operations, Name [Domain] Disposition Of Assets [Line Items] Disposition Of Assets [Line Items] Disposition Of Assets [Line Items] Document Documentand Entity Information [Abstract] Document Documentand Entity Information [Abstract] Document Documentand Entity Information [Abstract] Document Fiscal Period Focus Document Fiscal Period Focus Document Fiscal Year Focus Document Fiscal Year Focus