Segment Reporting - Reconciliation of Financial Measures of Segments to Consolidated Totals (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue, Major Customer [Line Items]
Revenues from customers	$ 66,852	$ 64,547	$ 198,602	$ 189,082
Net investment income	204	263	550	805
Total revenues	67,056	64,810	199,152	189,887
Adjusted operating income (loss)	3,622	3,947	13,063	11,573
Pharmacy Services
Revenue, Major Customer [Line Items]
Total revenues	35,711	36,018	105,583	104,418
Retail/ LTC
Revenue, Major Customer [Line Items]
Total revenues	22,725	21,466	67,136	64,028
Health Care Benefits
Revenue, Major Customer [Line Items]
Total revenues	18,698	17,181	56,364	52,454
Corporate/ Other
Revenue, Major Customer [Line Items]
Net investment income	83	117	209	347
Total revenues	116	152	292	423
Operating Segments | Pharmacy Services
Revenue, Major Customer [Line Items]
Revenues from customers	33,492	33,680	98,233	95,494
Net investment income	0	0	0	0
Total revenues	35,711	36,018	105,583	104,418
Adjusted operating income (loss)	1,619	1,439	4,127	3,682
Net revenues, retail copayments	2,500	2,700	8,500	8,900
Operating Segments | Retail/ LTC
Revenue, Major Customer [Line Items]
Revenues from customers	14,770	13,805	44,314	41,536
Net investment income	0	0	0	0
Total revenues	22,725	21,466	67,136	64,028
Adjusted operating income (loss)	1,412	1,516	4,371	4,674
Operating Segments | Health Care Benefits
Revenue, Major Customer [Line Items]
Revenues from customers	18,557	17,027	55,972	51,976
Net investment income	121	146	341	458
Total revenues	18,698	17,181	56,364	52,454
Adjusted operating income (loss)	1,080	1,423	6,035	4,423
Operating Segments | Corporate/ Other
Revenue, Major Customer [Line Items]
Revenues from customers	33	35	83	76
Adjusted operating income (loss)	(303)	(252)	(931)	(685)
Intersegment Eliminations
Revenue, Major Customer [Line Items]
Revenues	(10,194)	(10,007)	(30,223)	(31,436)
Net investment income	0	0	0	0
Total revenues	(10,194)	(10,007)	(30,223)	(31,436)
Adjusted operating income (loss)	(186)	(179)	(539)	(521)
Intersegment Eliminations | Pharmacy Services
Revenue, Major Customer [Line Items]
Revenues	2,219	2,338	7,350	8,924
Intersegment Eliminations | Retail/ LTC
Revenue, Major Customer [Line Items]
Revenues	7,955	7,661	22,822	22,492
Intersegment Eliminations | Health Care Benefits
Revenue, Major Customer [Line Items]
Revenues	20	8	51	20
Intersegment Eliminations | Corporate/ Other
Revenue, Major Customer [Line Items]
Revenues	$ 0	$ 0	$ 0	$ 0