Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Net investment income									$ 1,011	$ 660	$ 21
Total revenues	$ 66,889	$ 64,810	$ 63,431	$ 61,646	$ 54,424	$ 47,490	$ 46,922	$ 45,743	256,776	194,579	184,786
Pharmacy
Disaggregation of Revenue [Line Items]
Revenues									165,899	164,845
Front Store
Disaggregation of Revenue [Line Items]
Revenues									19,422	19,055
Premiums
Disaggregation of Revenue [Line Items]
Revenues									63,122	8,184
Other
Disaggregation of Revenue [Line Items]
Revenues									7,322	1,835
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Net investment income									0	0	0
Total revenues									(41,439)	(33,714)	(29,037)
Intersegment Eliminations | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues									(41,439)	(33,714)
Intersegment Eliminations | Front Store
Disaggregation of Revenue [Line Items]
Revenues									0	0
Intersegment Eliminations | Premiums
Disaggregation of Revenue [Line Items]
Revenues									0	0
Intersegment Eliminations | Other
Disaggregation of Revenue [Line Items]
Revenues									0	0
Pharmacy Services | Operating Segments
Disaggregation of Revenue [Line Items]
Net investment income									0	0	0
Total revenues									141,491	134,736	130,822
Pharmacy Services | Operating Segments | Pharmacy network
Disaggregation of Revenue [Line Items]
Total revenues									88,755	87,167
Pharmacy Services | Operating Segments | Mail choice
Disaggregation of Revenue [Line Items]
Total revenues									52,141	47,049
Pharmacy Services | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Total revenues									595	520
Pharmacy Services | Operating Segments | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues									140,896	134,216
Pharmacy Services | Operating Segments | Front Store
Disaggregation of Revenue [Line Items]
Revenues									0	0
Pharmacy Services | Operating Segments | Premiums
Disaggregation of Revenue [Line Items]
Revenues									0	0
Pharmacy Services | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Revenues									595	520
Retail/ LTC | Operating Segments
Disaggregation of Revenue [Line Items]
Net investment income									0	0	0
Total revenues									86,608	83,989	79,398
Retail/ LTC | Operating Segments | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues									66,442	64,179
Retail/ LTC | Operating Segments | Front Store
Disaggregation of Revenue [Line Items]
Revenues									19,422	19,055
Retail/ LTC | Operating Segments | Premiums
Disaggregation of Revenue [Line Items]
Revenues									0	0
Retail/ LTC | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Revenues									744	755
Health Care Benefits | Operating Segments
Disaggregation of Revenue [Line Items]
Net investment income									599	58	5
Total revenues									69,604	8,962	3,587
Health Care Benefits | Operating Segments | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues									0	164
Health Care Benefits | Operating Segments | Front Store
Disaggregation of Revenue [Line Items]
Revenues									0	0
Health Care Benefits | Operating Segments | Premiums
Disaggregation of Revenue [Line Items]
Revenues									63,031	8,180
Health Care Benefits | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Revenues									5,974	560
Corporate/ Other
Disaggregation of Revenue [Line Items]
Net investment income									412	602	16
Total revenues									512	606	$ 16
Corporate/ Other | Pharmacy
Disaggregation of Revenue [Line Items]
Revenues									0	0
Corporate/ Other | Front Store
Disaggregation of Revenue [Line Items]
Revenues									0	0
Corporate/ Other | Premiums
Disaggregation of Revenue [Line Items]
Revenues									91	4
Corporate/ Other | Other
Disaggregation of Revenue [Line Items]
Revenues									$ 9	$ 0