Accounting Policies - Description of Business (Details)	9 Months Ended
	Sep. 30, 2018 state segment clinic pharmacy item store Center
Segment reporting information
Number of reportable segments | segment	3
Pharmacy Services Segment
Segment reporting information
Number of pharmacies	68,000
Number of chain pharmacies	41,000
Number of independent pharmacies	27,000
Number of conditions for integrated disease management | item	19
Centers of excellence for infusion and enteral services | Center	3
Number of states pharmacies operated | state	42
Pharmacy Services Segment | Specialty stores
Segment reporting information
Number of pharmacies	25
Pharmacy Services Segment | Specialty mail order
Segment reporting information
Number of pharmacies	17
Pharmacy Services Segment | Mail service
Segment reporting information
Number of pharmacies	4
Pharmacy Services Segment | Infusion and Enteral Branches
Segment reporting information
Number of infusion and enteral branches	86
Pharmacy Services Segment | Ambulatory Infusion Suites
Segment reporting information
Number of infusion and enteral branches	68
Retail/LTC Segment
Segment reporting information
Number of states pharmacies operated | state	49
Number of drugstores | store	9,905
Number of on-site pharmacies	37
Number of LTC spoke pharmacies | store	155
Number of LTC hub pharmacies | store	30
Retail/LTC Segment | MinuteClinic
Segment reporting information
Number of drugstores | clinic	1,102
Retail/LTC Segment | Minute Clinic Within C V S Pharmacy Stores
Segment reporting information
Number of drugstores | clinic	1,098
Retail/LTC Segment | Pharmacy
Segment reporting information
Number of drugstores | store	8,149
Target Pharmacy Acquisition | Retail/LTC Segment
Segment reporting information
Number of pharmacies acquired	1,709