Accounting Policies - Description of Business (Details)	3 Months Ended
	Mar. 31, 2018 segment state clinic pharmacy item store Center
Segment reporting information
Number of reportable segments | segment	3
Pharmacy Services Segment
Segment reporting information
Number of pharmacies (more than 68,000)	68,000
Number of chain pharmacies	41,000
Number of independent pharmacies	27,000
Number of conditions for integrated disease management | item	18
Centers of excellence for infusion and enteral services | Center	3
Number of states pharmacies operated | state	43
Pharmacy Services Segment | Specialty stores
Segment reporting information
Number of pharmacies (more than 68,000)	25
Pharmacy Services Segment | Specialty mail order
Segment reporting information
Number of pharmacies (more than 68,000)	18
Pharmacy Services Segment | Mail service
Segment reporting information
Number of pharmacies (more than 68,000)	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	74
Retail/LTC Segment
Segment reporting information
Number of states pharmacies operated | state	49
Number of drugstores | store	9,847
Number of on-site pharmacies	37
Number of LTC spoke pharmacies | store	163
Number of LTC hub pharmacies | store	30
Retail/LTC Segment | MinuteClinic
Segment reporting information
Number of drugstores | clinic	1,111
Retail/LTC Segment | Minute Clinic Within C V S Pharmacy Stores
Segment reporting information
Number of drugstores | clinic	1,107
Retail/LTC Segment | Pharmacy
Segment reporting information
Number of drugstores | store	8,099
Target Pharmacy Acquisition | Retail/LTC Segment
Segment reporting information
Number of pharmacies acquired	1,699