Segment Reporting - Summarized Financial Information of Segments (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
Segment Reporting Information [Line Items]
Revenues from customers									$ 255,765	$ 193,919	$ 184,765
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
Adjusted operating income (loss)									15,339	11,261	10,825
Depreciation and amortization									4,371	2,718	2,479
Additions to property and equipment									2,481	2,123	2,049
Corporate/ Other
Segment Reporting Information [Line Items]
Revenues from customers									100	4	0
Net investment income									412	602	16
Total revenues									512	606	16
Adjusted operating income (loss)									(1,000)	(856)	(896)
Depreciation and amortization									161	138	116
Additions to property and equipment									404	401	340
Operating Segments | Pharmacy Services
Segment Reporting Information [Line Items]
Revenues from customers									141,491	134,736	130,822
Net investment income									0	0	0
Total revenues									141,491	134,736	130,822
Adjusted operating income (loss)									5,129	4,955	4,628
Depreciation and amortization									766	710	710
Additions to property and equipment									332	326	311
Co-payments									11,500	11,400	10,800
Operating Segments | Retail/ LTC
Segment Reporting Information [Line Items]
Revenues from customers									86,608	83,989	79,398
Net investment income									0	0	0
Total revenues									86,608	83,989	79,398
Adjusted operating income (loss)									6,705	7,403	7,475
Depreciation and amortization									1,723	1,698	1,651
Additions to property and equipment									1,212	1,350	1,398
Operating Segments | Health Care Benefits
Segment Reporting Information [Line Items]
Revenues from customers									69,005	8,904	3,582
Net investment income									599	58	5
Total revenues									69,604	8,962	3,587
Adjusted operating income (loss)									5,202	528	359
Depreciation and amortization									1,721	172	2
Additions to property and equipment									533	46	0
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues from customers									(41,439)	(33,714)	(29,037)
Net investment income									0	0	0
Total revenues									(41,439)	(33,714)	(29,037)
Adjusted operating income (loss)									(697)	(769)	(741)
Depreciation and amortization									0	0	0
Additions to property and equipment									$ 0	$ 0	$ 0