Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 68,800	$ 66,593
Net investment income	297	162
Total revenues	69,097	66,755
Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	42,952	41,872
Front Store
Disaggregation of Revenue [Line Items]
Revenues	4,642	5,208
Premiums
Disaggregation of Revenue [Line Items]
Revenues	18,960	17,640
Other
Disaggregation of Revenue [Line Items]
Revenues	2,246	1,873
Health Care Benefits
Disaggregation of Revenue [Line Items]
Total revenues	20,483	19,198
Pharmacy Services
Disaggregation of Revenue [Line Items]
Total revenues	36,321	34,983
Retail/ LTC
Disaggregation of Revenue [Line Items]
Total revenues	23,274	22,749
Operating Segments | Health Care Benefits
Disaggregation of Revenue [Line Items]
Revenues	20,315	19,097
Net investment income	148	93
Total revenues	20,483	19,198
Operating Segments | Health Care Benefits | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Health Care Benefits | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Health Care Benefits | Premiums
Disaggregation of Revenue [Line Items]
Revenues	18,942	17,621
Operating Segments | Health Care Benefits | Other
Disaggregation of Revenue [Line Items]
Revenues	1,393	1,484
Operating Segments | Pharmacy Services
Disaggregation of Revenue [Line Items]
Revenues	33,313	32,118
Net investment income	0	0
Total revenues	36,321	34,983
Operating Segments | Pharmacy Services | Pharmacy network
Disaggregation of Revenue [Line Items]
Total revenues	21,893	21,100
Operating Segments | Pharmacy Services | Mail choice
Disaggregation of Revenue [Line Items]
Total revenues	14,248	13,674
Operating Segments | Pharmacy Services | Other
Disaggregation of Revenue [Line Items]
Total revenues	180	209
Operating Segments | Pharmacy Services | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	36,141	34,774
Operating Segments | Pharmacy Services | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Pharmacy Services | Premiums
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Pharmacy Services | Other
Disaggregation of Revenue [Line Items]
Revenues	180	209
Operating Segments | Retail/ LTC
Disaggregation of Revenue [Line Items]
Revenues	15,140	15,357
Net investment income	46	0
Total revenues	23,274	22,749
Operating Segments | Retail/ LTC | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	17,885	17,355
Operating Segments | Retail/ LTC | Front Store
Disaggregation of Revenue [Line Items]
Revenues	4,642	5,208
Operating Segments | Retail/ LTC | Premiums
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Retail/ LTC | Other
Disaggregation of Revenue [Line Items]
Revenues	701	186
Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Revenues	32	21
Net investment income	103	69
Total revenues	135	90
Corporate, Non-Segment | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	0	0
Corporate, Non-Segment | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0
Corporate, Non-Segment | Premiums
Disaggregation of Revenue [Line Items]
Revenues	18	19
Corporate, Non-Segment | Other
Disaggregation of Revenue [Line Items]
Revenues	14	2
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Net investment income	0	0
Total revenues	(11,116)	(10,265)
Intersegment Eliminations | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	(11,074)	(10,257)
Intersegment Eliminations | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Premiums
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Other
Disaggregation of Revenue [Line Items]
Revenues	$ (42)	$ (8)