Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 73,548	$ 66,852	$ 214,675	$ 198,602
Net investment income (loss)	246	204	832	550
Total revenues	73,794	67,056	215,507	199,152
Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	47,033	43,062	135,917	126,725
Front Store
Disaggregation of Revenue [Line Items]
Revenues	5,359	4,740	15,255	14,601
Premiums
Disaggregation of Revenue [Line Items]
Revenues	18,984	17,182	56,927	51,749
Other
Disaggregation of Revenue [Line Items]
Revenues	2,172	1,868	6,576	5,527
Health Care Benefits
Disaggregation of Revenue [Line Items]
Total revenues	20,479	18,698	61,487	56,364
Pharmacy Services
Disaggregation of Revenue [Line Items]
Total revenues	39,046	35,711	113,681	105,583
Retail/ LTC
Disaggregation of Revenue [Line Items]
Total revenues	24,992	22,725	72,994	67,136
Operating Segments | Health Care Benefits
Disaggregation of Revenue [Line Items]
Revenues	20,311	18,557	60,993	55,972
Net investment income (loss)	147	121	432	341
Total revenues	20,479	18,698	61,487	56,364
Operating Segments | Health Care Benefits | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Health Care Benefits | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Health Care Benefits | Premiums
Disaggregation of Revenue [Line Items]
Revenues	18,959	17,165	56,869	51,699
Operating Segments | Health Care Benefits | Other
Disaggregation of Revenue [Line Items]
Revenues	1,373	1,412	4,186	4,324
Operating Segments | Pharmacy Services
Disaggregation of Revenue [Line Items]
Revenues	36,851	33,492	105,909	98,233
Net investment income (loss)	0	0	0	0
Total revenues	39,046	35,711	113,681	105,583
Operating Segments | Pharmacy Services | Pharmacy network
Disaggregation of Revenue [Line Items]
Total revenues	23,665	21,473	68,476	63,109
Operating Segments | Pharmacy Services | Mail choice
Disaggregation of Revenue [Line Items]
Total revenues	15,202	14,032	44,685	41,815
Operating Segments | Pharmacy Services | Other
Disaggregation of Revenue [Line Items]
Total revenues	179	206	520	659
Operating Segments | Pharmacy Services | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	38,867	35,505	113,161	104,924
Operating Segments | Pharmacy Services | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Pharmacy Services | Premiums
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Pharmacy Services | Other
Disaggregation of Revenue [Line Items]
Revenues	179	206	520	659
Operating Segments | Retail/ LTC
Disaggregation of Revenue [Line Items]
Revenues	16,347	14,770	47,672	44,314
Net investment income (loss)	(33)	0	13	0
Total revenues	24,992	22,725	72,994	67,136
Operating Segments | Retail/ LTC | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	19,023	17,608	55,781	51,833
Operating Segments | Retail/ LTC | Front Store
Disaggregation of Revenue [Line Items]
Revenues	5,359	4,740	15,255	14,601
Operating Segments | Retail/ LTC | Premiums
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Retail/ LTC | Other
Disaggregation of Revenue [Line Items]
Revenues	643	377	1,945	702
Corporate/ Other
Disaggregation of Revenue [Line Items]
Revenues	39	33	101	83
Net investment income (loss)	132	83	387	209
Total revenues	171	116	488	292
Corporate/ Other | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Corporate/ Other | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Corporate/ Other | Premiums
Disaggregation of Revenue [Line Items]
Revenues	25	17	58	50
Corporate/ Other | Other
Disaggregation of Revenue [Line Items]
Revenues	14	16	43	33
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Net investment income (loss)	0	0	0	0
Total revenues	(10,894)	(10,194)	(33,143)	(30,223)
Intersegment Eliminations | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	(10,857)	(10,051)	(33,025)	(30,032)
Intersegment Eliminations | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Premiums
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Other
Disaggregation of Revenue [Line Items]
Revenues	$ (37)	$ (143)	$ (118)	$ (191)