Segment Reporting - Reconciliation of Financial Measures of Segments to Consolidated Totals (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue, Major Customer [Line Items]
Revenues from customers	$ 63,138	$ 46,708	$ 124,535	$ 92,401
Net investment income	293	214	542	264
Total revenues	63,431	46,922	125,077	92,665
Adjusted operating income (loss)	4,031	2,599	7,626	4,892
Operating Segments | Pharmacy Services Segment
Revenue, Major Customer [Line Items]
Revenues from customers	34,842	33,427	68,400	65,973
Net investment income	0	0	0	0
Total revenues	34,842	33,427	68,400	65,973
Adjusted operating income (loss)	1,296	1,181	2,243	2,168
Net revenues, retail copayments	2,900	2,800	6,200	6,100
Operating Segments | Retail Long-Term Care Segment
Revenue, Major Customer [Line Items]
Revenues from customers	21,447	20,672	42,562	41,104
Net investment income	0	0	0	0
Total revenues	21,447	20,672	42,562	41,104
Adjusted operating income (loss)	1,669	1,821	3,158	3,657
Operating Segments | Health Care Benefits Segment
Revenue, Major Customer [Line Items]
Revenues from customers	17,255	760	34,961	2,076
Net investment income	148	4	312	6
Total revenues	17,403	764	35,273	2,082
Adjusted operating income (loss)	1,438	0	3,000	(137)
Operating Segments | Corporate / Other
Revenue, Major Customer [Line Items]
Revenues from customers	16	0	41	0
Net investment income	145	210	230	258
Total revenues	161	210	271	258
Adjusted operating income (loss)	(202)	(216)	(433)	(434)
Intersegment Eliminations
Revenue, Major Customer [Line Items]
Revenues from customers	(10,422)	(8,151)	(21,429)	(16,752)
Net investment income	0	0	0	0
Total revenues	(10,422)	(8,151)	(21,429)	(16,752)
Adjusted operating income (loss)	$ (170)	$ (187)	$ (342)	$ (362)