Segment Reporting - Retrospective Adjustment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Total revenues	$ 64,810	$ 47,490	$ 189,887	$ 140,155
Cost of products sold	40,437	39,502	116,654	115,883
Benefit costs	12,850	439	39,396	2,399
Operating expenses	8,595	4,975	24,887	14,755
Operating income (GAAP measure)	2,928	2,574	8,950	3,197
Adjusted operating income (loss)	3,947	2,650	11,573	7,542
Operating Segments | Pharmacy Services Segment
Segment Reporting Information [Line Items]
Total revenues	36,018	33,864	104,418	99,837
Cost of products sold		32,238		95,518
Benefit costs		0		0
Operating expenses		351		1,051
Operating income (GAAP measure)		1,275		3,268
Adjusted operating income (loss)	1,439	1,362	3,682	3,530
Operating Segments | Retail Long-Term Care Segment
Segment Reporting Information [Line Items]
Total revenues	21,466	20,856	64,028	61,960
Cost of products sold		15,042		44,318
Benefit costs		0		0
Operating expenses		4,323		12,831
Operating income (GAAP measure)		1,491		890
Adjusted operating income (loss)	1,516	1,622	4,674	5,279
Operating Segments | Health Care Benefits Segment
Segment Reporting Information [Line Items]
Total revenues	17,181	641	52,454	2,723
Cost of products sold		0		0
Benefit costs		439		2,399
Operating expenses		128		388
Operating income (GAAP measure)		74		(64)
Adjusted operating income (loss)	1,423	75	4,423	(62)
Operating Segments | Corporate / Other
Segment Reporting Information [Line Items]
Total revenues	152	217	423	475
Cost of products sold		0		0
Benefit costs		0		0
Operating expenses		287		814
Operating income (GAAP measure)		(70)		(339)
Adjusted operating income (loss)	(252)	(213)	(685)	(647)
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenues	(10,007)	(8,088)	(31,436)	(24,840)
Cost of products sold		(7,778)		(23,953)
Benefit costs		0		0
Operating expenses		(114)		(329)
Operating income (GAAP measure)		(196)		(558)
Adjusted operating income (loss)	$ (179)	(196)	$ (521)	(558)
Previously Reported
Segment Reporting Information [Line Items]
Total revenues		47,490		140,155
Cost of products sold		39,502		115,883
Benefit costs		439		2,399
Operating expenses		4,975		14,755
Operating income (GAAP measure)		2,574		3,197
Previously Reported | Operating Segments | Pharmacy Services Segment
Segment Reporting Information [Line Items]
Total revenues		33,767		99,238
Cost of products sold		31,587		92,459
Benefit costs		439		2,399
Operating expenses		392		1,176
Operating income (GAAP measure)		1,349		3,204
Previously Reported | Operating Segments | Retail Long-Term Care Segment
Segment Reporting Information [Line Items]
Total revenues		20,856		61,960
Cost of products sold		15,042		44,318
Benefit costs		0		0
Operating expenses		4,323		12,831
Operating income (GAAP measure)		1,491		890
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 (GAAP measure)		0		0
Previously Reported | Operating Segments | Corporate / Other
Segment Reporting Information [Line Items]
Total revenues		217		475
Cost of products sold		0		0
Benefit costs		0		0
Operating expenses		287		814
Operating income (GAAP measure)		(70)		(339)
Previously Reported | Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenues		(7,350)		(21,518)
Cost of products sold		(7,127)		(20,894)
Benefit costs		0		0
Operating expenses		(27)		(66)
Operating income (GAAP measure)		(196)		(558)
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 (GAAP measure)		0		0
Adjusted operating income (loss)		76		4,345
Restatement Adjustment | Operating Segments | Pharmacy Services Segment
Segment Reporting Information [Line Items]
Total revenues		97		599
Cost of products sold		651		3,059
Benefit costs		(439)		(2,399)
Operating expenses		(41)		(125)
Operating income (GAAP measure)		(74)		64
Adjusted operating income (loss)		87		262
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 (GAAP measure)		0		0
Adjusted operating income (loss)		131		4,389
Restatement Adjustment | Operating Segments | Health Care Benefits Segment
Segment Reporting Information [Line Items]
Total revenues		641		2,723
Cost of products sold		0		0
Benefit costs		439		2,399
Operating expenses		128		388
Operating income (GAAP measure)		74		(64)
Adjusted operating income (loss)		1		2
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 (GAAP measure)		0		0
Adjusted operating income (loss)		(143)		(308)
Restatement Adjustment | Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenues		(738)		(3,322)
Cost of products sold		(651)		(3,059)
Benefit costs		0		0
Operating expenses		(87)		(263)
Operating income (GAAP measure)		0		0
Adjusted operating income (loss)		$ 0		$ 0