Segment Reporting - Summarized Financial Information of Segments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues from external customers	$ 267,908	$ 255,765	$ 193,919
Net investment income	798	1,011	660
Total revenues	268,706	256,776	194,579
Adjusted operating income (loss)	16,008	15,339	11,261
Depreciation and amortization	4,441	4,371	2,718
Operating Segments | Pharmacy Services
Segment Reporting Information [Line Items]
Revenues from external customers	132,663	130,428	130,012
Net investment income	0	0	0
Total revenues	141,938	141,491	134,736
Adjusted operating income (loss)	5,688	5,129	4,955
Depreciation and amortization	612	766	710
Co-payments	10,900	11,500	11,400
Operating Segments | Retail/ LTC
Segment Reporting Information [Line Items]
Revenues from external customers	60,208	56,258	54,999
Net investment income	0	0	0
Total revenues	91,198	86,608	83,989
Adjusted operating income (loss)	6,146	6,705	7,403
Depreciation and amortization	1,801	1,723	1,698
Operating Segments | Health Care Benefits
Segment Reporting Information [Line Items]
Revenues from external customers	74,926	68,979	8,904
Net investment income	483	599	58
Total revenues	75,467	69,604	8,962
Adjusted operating income (loss)	6,188	5,202	528
Depreciation and amortization	1,832	1,721	172
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	(40,323)	(41,439)	(33,714)
Net investment income	0	0	0
Total revenues	(40,323)	(41,439)	(33,714)
Adjusted operating income (loss)	(708)	(697)	(769)
Depreciation and amortization	0	0	0
Intersegment Eliminations | Pharmacy Services
Segment Reporting Information [Line Items]
Revenues	9,275	11,063	4,724
Intersegment Eliminations | Retail/ LTC
Segment Reporting Information [Line Items]
Revenues	30,990	30,350	28,990
Intersegment Eliminations | Health Care Benefits
Segment Reporting Information [Line Items]
Revenues	58	26	0
Corporate/ Other
Segment Reporting Information [Line Items]
Revenues from external customers	111	100	4
Net investment income	315	412	602
Total revenues	426	512	606
Adjusted operating income (loss)	(1,306)	(1,000)	(856)
Depreciation and amortization	$ 196	$ 161	$ 138