Segment Reporting - Reconciliation of Financial Measures of Segments to Consolidated Totals (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue, Major Customer [Line Items]
Revenues from customers	$ 65,157	$ 63,138	$ 131,750	$ 124,535
Net investment income	184	293	346	542
Total revenues	65,341	63,431	132,096	125,077
Adjusted operating income (loss)	5,328	4,031	9,441	7,626
Pharmacy Services
Revenue, Major Customer [Line Items]
Total revenues	34,889	34,842	69,872	68,400
Retail/ LTC
Revenue, Major Customer [Line Items]
Total revenues	21,662	21,447	44,411	42,562
Health Care Benefits
Revenue, Major Customer [Line Items]
Total revenues	18,468	17,403	37,666	35,273
Corporate/ Other
Revenue, Major Customer [Line Items]
Net investment income	57	145	126	230
Total revenues	86	161	176	271
Operating Segments | Pharmacy Services
Revenue, Major Customer [Line Items]
Revenues from customers	32,623	31,988	64,741	61,814
Net investment income	0	0	0	0
Total revenues	34,889	34,842	69,872	68,400
Adjusted operating income (loss)	1,327	1,296	2,508	2,243
Net revenues, retail copayments	2,600	2,900	6,000	6,200
Operating Segments | Retail/ LTC
Revenue, Major Customer [Line Items]
Revenues from customers	14,187	13,885	29,544	27,731
Net investment income	0	0	0	0
Total revenues	21,662	21,447	44,411	42,562
Adjusted operating income (loss)	1,057	1,669	2,959	3,158
Operating Segments | Health Care Benefits
Revenue, Major Customer [Line Items]
Revenues from customers	18,318	17,249	37,415	34,949
Net investment income	127	148	220	312
Total revenues	18,468	17,403	37,666	35,273
Adjusted operating income (loss)	3,464	1,438	4,955	3,000
Operating Segments | Corporate/ Other
Revenue, Major Customer [Line Items]
Revenues from customers	29	16	50	41
Adjusted operating income (loss)	(343)	(202)	(628)	(433)
Intersegment Eliminations
Revenue, Major Customer [Line Items]
Revenues	(9,764)	(10,422)	(20,029)	(21,429)
Net investment income	0	0	0	0
Total revenues	(9,764)	(10,422)	(20,029)	(21,429)
Adjusted operating income (loss)	(177)	(170)	(353)	(342)
Intersegment Eliminations | Pharmacy Services
Revenue, Major Customer [Line Items]
Revenues	2,266	2,854	5,131	6,586
Intersegment Eliminations | Retail/ LTC
Revenue, Major Customer [Line Items]
Revenues	7,475	7,562	14,867	14,831
Intersegment Eliminations | Health Care Benefits
Revenue, Major Customer [Line Items]
Revenues	23	6	31	12
Intersegment Eliminations | Corporate/ Other
Revenue, Major Customer [Line Items]
Revenues	$ 0	$ 0	$ 0	$ 0