Segment Reporting - Retrospective Adjustment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Total revenues	$ 63,431	$ 46,922	$ 125,077	$ 92,665
Cost of products sold	38,970	38,876	76,217	76,381
Benefit costs	13,087	631	26,546	1,960
Operating expenses	8,042	4,867	16,292	9,780
Operating income (loss) (GAAP measure)	3,332	(1,373)	6,022	623
Adjusted operating income (loss)	4,031	2,599	7,626	4,892
Operating Segments | Pharmacy Services Segment
Segment Reporting Information [Line Items]
Total revenues	34,842	33,427	68,400	65,973
Cost of products sold		31,973		63,280
Benefit costs		0		0
Operating expenses		362		700
Operating income (loss) (GAAP measure)		1,092		1,993
Adjusted operating income (loss)	1,296	1,181	2,243	2,168
Operating Segments | Retail Long-Term Care Segment
Segment Reporting Information [Line Items]
Total revenues	21,447	20,672	42,562	41,104
Cost of products sold		14,760		29,276
Benefit costs		0		0
Operating expenses		4,216		8,508
Operating income (loss) (GAAP measure)		(2,225)		(601)
Adjusted operating income (loss)	1,669	1,821	3,158	3,657
Operating Segments | Health Care Benefits Segment
Segment Reporting Information [Line Items]
Total revenues	17,403	764	35,273	2,082
Cost of products sold		0		0
Benefit costs		631		1,960
Operating expenses		133		260
Operating income (loss) (GAAP measure)		0		(138)
Adjusted operating income (loss)	1,438	0	3,000	(137)
Operating Segments | Corporate / Other
Segment Reporting Information [Line Items]
Total revenues	161	210	271	258
Cost of products sold		0		0
Benefit costs		0		0
Operating expenses		263		527
Operating income (loss) (GAAP measure)		(53)		(269)
Adjusted operating income (loss)	(202)	(216)	(433)	(434)
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenues	(10,422)	(8,151)	(21,429)	(16,752)
Cost of products sold		(7,857)		(16,175)
Benefit costs		0		0
Operating expenses		(107)		(215)
Operating income (loss) (GAAP measure)		(187)		(362)
Adjusted operating income (loss)	$ (170)	(187)	$ (342)	(362)
Previously Reported
Segment Reporting Information [Line Items]
Total revenues		46,922		92,665
Cost of products sold		38,876		76,381
Benefit costs		631		1,960
Operating expenses		4,867		9,780
Operating income (loss) (GAAP measure)		(1,373)		623
Previously Reported | Operating Segments | Pharmacy Services Segment
Segment Reporting Information [Line Items]
Total revenues		33,251		65,471
Cost of products sold		31,121		60,872
Benefit costs		631		1,960
Operating expenses		407		784
Operating income (loss) (GAAP measure)		1,092		1,855
Previously Reported | Operating Segments | Retail Long-Term Care Segment
Segment Reporting Information [Line Items]
Total revenues		20,672		41,104
Cost of products sold		14,760		29,276
Benefit costs		0		0
Operating expenses		4,216		8,508
Operating income (loss) (GAAP measure)		(2,225)		(601)
Previously Reported | Operating Segments | Health Care Benefits Segment
Segment Reporting Information [Line Items]
Total revenues		0		0
Cost of products sold		0		0
Benefit costs		0		0
Operating expenses		0		0
Operating income (loss) (GAAP measure)		0		0
Previously Reported | Operating Segments | Corporate / Other
Segment Reporting Information [Line Items]
Total revenues		210		258
Cost of products sold		0		0
Benefit costs		0		0
Operating expenses		263		527
Operating income (loss) (GAAP measure)		(53)		(269)
Previously Reported | Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenues		(7,211)		(14,168)
Cost of products sold		(7,005)		(13,767)
Benefit costs		0		0
Operating expenses		(19)		(39)
Operating income (loss) (GAAP measure)		(187)		(362)
Restatement Adjustment
Segment Reporting Information [Line Items]
Total revenues		0		0
Cost of products sold		0		0
Benefit costs		0		0
Operating expenses		0		0
Operating income (loss) (GAAP measure)		0		0
Adjusted operating income (loss)		3,972		4,269
Restatement Adjustment | Operating Segments | Pharmacy Services Segment
Segment Reporting Information [Line Items]
Total revenues		176		502
Cost of products sold		852		2,408
Benefit costs		(631)		(1,960)
Operating expenses		(45)		(84)
Operating income (loss) (GAAP measure)		0		138
Adjusted operating income (loss)		89		175
Restatement Adjustment | Operating Segments | Retail Long-Term Care Segment
Segment Reporting Information [Line Items]
Total revenues		0		0
Cost of products sold		0		0
Benefit costs		0		0
Operating expenses		0		0
Operating income (loss) (GAAP measure)		0		0
Adjusted operating income (loss)		4,046		4,258
Restatement Adjustment | Operating Segments | Health Care Benefits Segment
Segment Reporting Information [Line Items]
Total revenues		764		2,082
Cost of products sold		0		0
Benefit costs		631		1,960
Operating expenses		133		260
Operating income (loss) (GAAP measure)		0		(138)
Adjusted operating income (loss)		0		1
Restatement Adjustment | Operating Segments | Corporate / Other
Segment Reporting Information [Line Items]
Total revenues		0		0
Cost of products sold		0		0
Benefit costs		0		0
Operating expenses		0		0
Operating income (loss) (GAAP measure)		0		0
Adjusted operating income (loss)		(163)		(165)
Restatement Adjustment | Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenues		(940)		(2,584)
Cost of products sold		(852)		(2,408)
Benefit costs		0		0
Operating expenses		(88)		(176)
Operating income (loss) (GAAP measure)		0		0
Adjusted operating income (loss)		$ 0		$ 0