Accounting Policies - Revenue Disaggregation (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Revenue Disaggregation
Net revenue	$ 46,708	$ 92,401
Pharmacy
Revenue Disaggregation
Net revenue	40,947	80,252
Front Store
Revenue Disaggregation
Net revenue	4,707	9,433
Other
Revenue Disaggregation
Net revenue	1,054	2,716
Operating Segments | Pharmacy Services Segment
Revenue Disaggregation
Net revenue	33,247	65,465
Operating Segments | Pharmacy Services Segment | Pharmacy
Revenue Disaggregation
Net revenue	32,353	63,115
Operating Segments | Pharmacy Services Segment | Mail choice
Revenue Disaggregation
Net revenue	11,787	22,995
Operating Segments | Pharmacy Services Segment | Pharmacy network
Revenue Disaggregation
Net revenue	20,566	40,120
Operating Segments | Pharmacy Services Segment | Other
Revenue Disaggregation
Net revenue	894	2,350
Operating Segments | Retail/LTC Segment
Revenue Disaggregation
Net revenue	20,672	41,104
Operating Segments | Retail/LTC Segment | Pharmacy
Revenue Disaggregation
Net revenue	15,805	31,305
Operating Segments | Retail/LTC Segment | Front Store
Revenue Disaggregation
Net revenue	4,707	9,433
Operating Segments | Retail/LTC Segment | Other
Revenue Disaggregation
Net revenue	160	366
Intersegment Eliminations
Revenue Disaggregation
Net revenue	(7,211)	(14,168)
Intersegment Eliminations | Pharmacy
Revenue Disaggregation
Net revenue	$ (7,211)	$ (14,168)