Segment Reporting - Reconciliation of Financial Measures of Segments to Consolidated Totals (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue, Major Customer [Line Items]
Revenues from customers	$ 66,593	$ 61,397
Net investment income	162	249
Total revenues	66,755	61,646
Adjusted operating income (loss)	4,113	3,595
Pharmacy Services
Revenue, Major Customer [Line Items]
Total revenues	34,983	33,558
Retail/ LTC
Revenue, Major Customer [Line Items]
Total revenues	22,749	21,115
Health Care Benefits
Revenue, Major Customer [Line Items]
Total revenues	19,198	17,870
Corporate/ Other
Revenue, Major Customer [Line Items]
Net investment income	69	85
Total revenues	90	110
Operating Segments | Pharmacy Services
Revenue, Major Customer [Line Items]
Revenues from customers	32,118	29,826
Net investment income	0	0
Total revenues	34,983	33,558
Adjusted operating income (loss)	1,181	947
Net revenues, retail copayments	3,400	3,300
Operating Segments | Retail/ LTC
Revenue, Major Customer [Line Items]
Revenues from customers	15,357	13,846
Net investment income	0	0
Total revenues	22,749	21,115
Adjusted operating income (loss)	1,902	1,489
Operating Segments | Health Care Benefits
Revenue, Major Customer [Line Items]
Revenues from customers	19,097	17,700
Net investment income	93	164
Total revenues	19,198	17,870
Adjusted operating income (loss)	1,491	1,562
Operating Segments | Corporate/ Other
Revenue, Major Customer [Line Items]
Revenues from customers	21	25
Adjusted operating income (loss)	(285)	(231)
Intersegment Eliminations
Revenue, Major Customer [Line Items]
Revenues	(10,265)	(11,007)
Net investment income	0	0
Total revenues	(10,265)	(11,007)
Adjusted operating income (loss)	(176)	(172)
Intersegment Eliminations | Pharmacy Services
Revenue, Major Customer [Line Items]
Revenues	2,865	3,732
Intersegment Eliminations | Retail/ LTC
Revenue, Major Customer [Line Items]
Revenues	7,392	7,269
Intersegment Eliminations | Health Care Benefits
Revenue, Major Customer [Line Items]
Revenues	8	6
Intersegment Eliminations | Corporate/ Other
Revenue, Major Customer [Line Items]
Revenues	$ 0	$ 0