Segment Reporting (Details) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)
Segment reporting information
Number of operating segments | segment				2
Number of reportable segments | segment				3
Net revenues	$ 47,269		$ 46,181	$ 139,670	$ 136,380
Cost of revenue	39,941		39,064	118,282	115,766
Gross profit	7,328		7,117	21,388	20,614
Operating expenses			4,618		14,205
Operating profit (loss)	2,353		2,499	2,712	6,409
Goodwill, impairment loss				3,921	135
Pharmacy Services Segment
Segment reporting information
Net revenues, retail co-payments	2,700		2,600	8,800	8,400
Retail/LTC Segment
Segment reporting information
Goodwill, impairment loss				3,921
Loss on disposal				86
Retail/LTC Segment | Operating profit
Segment reporting information
Restructuring Charges			6		211
Rx Crossroads
Segment reporting information
Goodwill, impairment loss					135
LTC reporting unit
Segment reporting information
Goodwill, impairment loss		$ 3,900
LTC reporting unit | Operating profit
Segment reporting information
Goodwill, impairment loss				3,900
Operating Segments | Pharmacy Services Segment
Segment reporting information
Net revenues	33,763		32,896	99,228	96,444
Cost of revenue			31,264		92,273
Gross profit	1,737		1,632	4,370	4,171
Operating expenses			305		975
Operating profit (loss)	1,345		1,327	3,194	3,196
Operating Segments | Retail/LTC Segment
Segment reporting information
Net revenues	20,856		19,593	61,960	58,488
Cost of revenue			13,904		41,440
Gross profit	5,814		5,689	17,642	17,048
Operating expenses			4,108		12,606
Operating profit (loss)	1,491		1,581	890	4,442
Operating Segments | Corporate Segment
Segment reporting information
Operating expenses			222		677
Operating profit (loss)	(287)		(222)	(814)	(677)
Intersegment Eliminations
Segment reporting information
Net revenues	(7,350)		(6,308)	(21,518)	(18,552)
Cost of revenue			(6,104)		(17,947)
Gross profit	(223)		(204)	(624)	(605)
Operating expenses			(17)		(53)
Operating profit (loss)	(196)		(187)	(558)	(552)
Previously Reported
Segment reporting information
Cost of revenue			39,055		115,739
Gross profit			7,126		20,641
Operating expenses			4,627		14,232
Operating profit (loss)			2,499		6,409
Previously Reported | Operating Segments | Pharmacy Services Segment
Segment reporting information
Cost of revenue			31,251		92,234
Gross profit			1,645		4,210
Operating expenses			292		938
Operating profit (loss)			1,353		3,272
Previously Reported | Operating Segments | Retail/LTC Segment
Segment reporting information
Cost of revenue			13,908		41,452
Gross profit			5,685		17,036
Operating expenses			4,132		12,661
Operating profit (loss)			1,553		4,375
Previously Reported | Operating Segments | Corporate Segment
Segment reporting information
Operating expenses			220		686
Operating profit (loss)			(220)		(686)
Previously Reported | Intersegment Eliminations
Segment reporting information
Cost of revenue			(6,104)		(17,947)
Gross profit			(204)		(605)
Operating expenses			(17)		(53)
Operating profit (loss)			(187)		(552)
Adjustments.
Segment reporting information
Cost of revenue			9		27
Gross profit			(9)		(27)
Operating expenses			(9)		(27)
Adjustments. | Operating Segments | Pharmacy Services Segment
Segment reporting information
Cost of revenue			13		39
Gross profit			(13)		(39)
Operating expenses			13		37
Operating profit (loss)			(26)		(76)
Adjustments. | Operating Segments | Retail/LTC Segment
Segment reporting information
Cost of revenue			(4)		(12)
Gross profit			4		12
Operating expenses			(24)		(55)
Operating profit (loss)			28		67
Adjustments. | Operating Segments | Corporate Segment
Segment reporting information
Operating expenses			2		(9)
Operating profit (loss)			(2)		9
Omnicare, Inc. | Retail/LTC Segment | Gross Profit
Segment reporting information
Acquisition related costs			2		7
Omnicare, Inc. | Retail/LTC Segment | Operating profit
Segment reporting information
Integration related costs	4		9	7	34
Omnicare, Inc. | Corporate Segment | Operating profit
Segment reporting information
Business Combination Acquisition Related Costs And Integration Related Costs			$ 3		$ 3
Aetna Acquisition | Corporate Segment | Operating profit
Segment reporting information
Business Combination Acquisition Related Costs And Integration Related Costs	$ 66			$ 145