Accounting Policies - Revenue Disaggregation (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Revenue Disaggregation
Net revenue	$ 47,269	$ 139,670
Pharmacy
Revenue Disaggregation
Net revenue	41,768	122,020
Front Store
Revenue Disaggregation
Net revenue	4,557	13,990
Other
Revenue Disaggregation
Net revenue	944	3,660
Operating Segments | Pharmacy Services Segment
Revenue Disaggregation
Net revenue	33,763	99,228
Operating Segments | Pharmacy Services Segment | Pharmacy
Revenue Disaggregation
Net revenue	32,995	96,110
Operating Segments | Pharmacy Services Segment | Mail choice
Revenue Disaggregation
Net revenue	11,812	34,807
Operating Segments | Pharmacy Services Segment | Pharmacy network
Revenue Disaggregation
Net revenue	21,183	61,303
Operating Segments | Pharmacy Services Segment | Other
Revenue Disaggregation
Net revenue	768	3,118
Operating Segments | Retail/LTC Segment
Revenue Disaggregation
Net revenue	20,856	61,960
Operating Segments | Retail/LTC Segment | Pharmacy
Revenue Disaggregation
Net revenue	16,123	47,428
Operating Segments | Retail/LTC Segment | Front Store
Revenue Disaggregation
Net revenue	4,557	13,990
Operating Segments | Retail/LTC Segment | Other
Revenue Disaggregation
Net revenue	176	542
Intersegment Eliminations
Revenue Disaggregation
Net revenue	(7,350)	(21,518)
Intersegment Eliminations | Pharmacy
Revenue Disaggregation
Net revenue	$ (7,350)	$ (21,518)