Segment Reporting - Reconciliation of Financial Measures of Segments to Consolidated Totals (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue, Major Customer [Line Items]
Revenues from external customers	$ 68,800	$ 66,593
Net investment income	297	162
Total revenues	69,097	66,755
Adjusted operating income (loss)	4,205	4,113
Health Care Benefits
Revenue, Major Customer [Line Items]
Total revenues	20,483	19,198
Pharmacy Services
Revenue, Major Customer [Line Items]
Total revenues	36,321	34,983
Retail/ LTC
Revenue, Major Customer [Line Items]
Total revenues	23,274	22,749
Operating Segments | Health Care Benefits
Revenue, Major Customer [Line Items]
Revenues from external customers	20,315	19,097
Net investment income	148	93
Total revenues	20,483	19,198
Adjusted operating income (loss)	1,782	1,491
Operating Segments | Pharmacy Services
Revenue, Major Customer [Line Items]
Revenues from external customers	33,313	32,118
Net investment income	0	0
Total revenues	36,321	34,983
Adjusted operating income (loss)	1,507	1,181
Copayments	3,400
Operating Segments | Retail/ LTC
Revenue, Major Customer [Line Items]
Revenues from external customers	15,140	15,357
Net investment income	46	0
Total revenues	23,274	22,749
Adjusted operating income (loss)	1,394	1,902
Intersegment Eliminations
Revenue, Major Customer [Line Items]
Revenues	(11,116)	(10,265)
Net investment income	0	0
Total revenues	(11,116)	(10,265)
Adjusted operating income (loss)	(175)	(176)
Intersegment Eliminations | Health Care Benefits
Revenue, Major Customer [Line Items]
Revenues	20	8
Intersegment Eliminations | Pharmacy Services
Revenue, Major Customer [Line Items]
Revenues	3,008	2,865
Intersegment Eliminations | Retail/ LTC
Revenue, Major Customer [Line Items]
Revenues	8,088	7,392
Corporate, Non-Segment
Revenue, Major Customer [Line Items]
Revenues from external customers	32	21
Net investment income	103	69
Total revenues	135	90
Adjusted operating income (loss)	$ (303)	$ (285)