Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 267,908	$ 255,765	$ 193,919
Net investment income	798	1,011	660
Total revenues	268,706	256,776	194,579
Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	171,289	165,925	164,845
Front Store
Disaggregation of Revenue [Line Items]
Revenues	19,655	19,422	19,055
Premiums
Disaggregation of Revenue [Line Items]
Revenues	69,364	63,122	8,184
Other
Disaggregation of Revenue [Line Items]
Revenues	7,600	7,296	1,835
Operating Segments | Pharmacy Services
Disaggregation of Revenue [Line Items]
Revenues	132,663	130,428	130,012
Net investment income	0	0	0
Total revenues	141,938	141,491	134,736
Operating Segments | Pharmacy Services | Pharmacy network
Disaggregation of Revenue [Line Items]
Total revenues	85,045	88,755	87,167
Operating Segments | Pharmacy Services | Mail choice
Disaggregation of Revenue [Line Items]
Total revenues	56,071	52,141	47,049
Operating Segments | Pharmacy Services | Other
Disaggregation of Revenue [Line Items]
Total revenues	822	595	520
Operating Segments | Pharmacy Services | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	141,116	140,896	134,216
Operating Segments | Pharmacy Services | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Operating Segments | Pharmacy Services | Premiums
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Operating Segments | Pharmacy Services | Other
Disaggregation of Revenue [Line Items]
Revenues	822	595	520
Operating Segments | Retail/ LTC
Disaggregation of Revenue [Line Items]
Revenues	60,208	56,258	54,999
Net investment income	0	0	0
Total revenues	91,198	86,608	83,989
Operating Segments | Retail/ LTC | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	70,176	66,442	64,179
Operating Segments | Retail/ LTC | Front Store
Disaggregation of Revenue [Line Items]
Revenues	19,655	19,422	19,055
Operating Segments | Retail/ LTC | Premiums
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Operating Segments | Retail/ LTC | Other
Disaggregation of Revenue [Line Items]
Revenues	1,367	744	755
Operating Segments | Health Care Benefits
Disaggregation of Revenue [Line Items]
Revenues	74,926	68,979	8,904
Net investment income	483	599	58
Total revenues	75,467	69,604	8,962
Operating Segments | Health Care Benefits | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	0	0	164
Operating Segments | Health Care Benefits | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Operating Segments | Health Care Benefits | Premiums
Disaggregation of Revenue [Line Items]
Revenues	69,301	63,031	8,180
Operating Segments | Health Care Benefits | Other
Disaggregation of Revenue [Line Items]
Revenues	5,683	5,974	560
Corporate/ Other
Disaggregation of Revenue [Line Items]
Revenues	111	100	4
Net investment income	315	412	602
Total revenues	426	512	606
Corporate/ Other | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Corporate/ Other | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Corporate/ Other | Premiums
Disaggregation of Revenue [Line Items]
Revenues	63	91	4
Corporate/ Other | Other
Disaggregation of Revenue [Line Items]
Revenues	48	9	0
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Net investment income	0	0	0
Total revenues	(40,323)	(41,439)	(33,714)
Intersegment Eliminations | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	(40,003)	(41,413)	(33,714)
Intersegment Eliminations | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Intersegment Eliminations | Premiums
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Intersegment Eliminations | Other
Disaggregation of Revenue [Line Items]
Revenues	$ (320)	$ (26)	$ 0