Segment Reporting - Reconciliation of Financial Measures of Segments to Consolidated Totals (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue, Major Customer [Line Items]
Revenues from customers	$ 64,547	$ 47,269	$ 189,082	$ 139,670
Net investment income	263	221	805	485
Total revenues	64,810	47,490	189,887	140,155
Adjusted operating income (loss)	3,947	2,650	11,573	7,542
Operating Segments | Pharmacy Services Segment
Revenue, Major Customer [Line Items]
Revenues from customers	36,018	33,864	104,418	99,837
Net investment income	0	0	0	0
Total revenues	36,018	33,864	104,418	99,837
Adjusted operating income (loss)	1,439	1,362	3,682	3,530
Net revenues, retail copayments	2,700	2,700	8,900	8,800
Operating Segments | Retail Long-Term Care Segment
Revenue, Major Customer [Line Items]
Revenues from customers	21,466	20,856	64,028	61,960
Net investment income	0	0	0	0
Total revenues	21,466	20,856	64,028	61,960
Adjusted operating income (loss)	1,516	1,622	4,674	5,279
Operating Segments | Health Care Benefits Segment
Revenue, Major Customer [Line Items]
Revenues from customers	17,035	637	51,996	2,713
Net investment income	146	4	458	10
Total revenues	17,181	641	52,454	2,723
Adjusted operating income (loss)	1,423	75	4,423	(62)
Operating Segments | Corporate / Other
Revenue, Major Customer [Line Items]
Revenues from customers	35	0	76	0
Net investment income	117	217	347	475
Total revenues	152	217	423	475
Adjusted operating income (loss)	(252)	(213)	(685)	(647)
Intersegment Eliminations
Revenue, Major Customer [Line Items]
Revenues from customers	(10,007)	(8,088)	(31,436)	(24,840)
Net investment income	0	0	0	0
Total revenues	(10,007)	(8,088)	(31,436)	(24,840)
Adjusted operating income (loss)	$ (179)	$ (196)	$ (521)	$ (558)