Segment Reporting (Details)	3 Months Ended			6 Months Ended
	Jun. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)
Segment reporting information
Number of operating segments | segment				2
Number of reportable segments | segment				3
Net revenues	$ 46,708,000,000		$ 45,685,000,000	$ 92,401,000,000	$ 90,199,000,000
Cost of revenue	39,507,000,000		38,759,000,000	78,341,000,000	76,702,000,000
Gross profit	7,201,000,000		6,926,000,000	14,060,000,000	13,497,000,000
Operating expenses			4,809,000,000		9,587,000,000
Operating profit (loss)	(1,587,000,000)		2,117,000,000	359,000,000	3,910,000,000
Goodwill, impairment loss	3,921,000,000	$ 0	135,000,000	3,921,000,000	135,000,000
Pharmacy Services Segment
Segment reporting information
Net revenues, retail co-payments	2,800,000,000		2,700,000,000	6,100,000,000	5,800,000,000
Retail/LTC Segment
Segment reporting information
Goodwill, impairment loss				3,921,000,000
Loss on disposal				86,000,000
Retail/LTC Segment | Operating profit
Segment reporting information
Restructuring Charges			6,000,000		205,000,000
Rx Crossroads
Segment reporting information
Goodwill, impairment loss			135,000,000		135,000,000
LTC reporting unit
Segment reporting information
Goodwill, impairment loss	3,900,000,000			3,900,000,000
LTC reporting unit | Operating profit
Segment reporting information
Goodwill, impairment loss	3,900,000,000			3,900,000,000
Operating Segments | Pharmacy Services Segment
Segment reporting information
Net revenues	33,247,000,000		32,325,000,000	65,465,000,000	63,548,000,000
Cost of revenue			30,868,000,000		61,009,000,000
Gross profit	1,495,000,000		1,457,000,000	2,633,000,000	2,539,000,000
Operating expenses			345,000,000		670,000,000
Operating profit (loss)	1,088,000,000		1,112,000,000	1,849,000,000	1,869,000,000
Operating Segments | Retail/LTC Segment
Segment reporting information
Net revenues	20,672,000,000		19,554,000,000	41,104,000,000	38,895,000,000
Cost of revenue			13,876,000,000		27,536,000,000
Gross profit	5,912,000,000		5,678,000,000	11,828,000,000	11,359,000,000
Operating expenses			4,250,000,000		8,498,000,000
Operating profit (loss)	(2,225,000,000)		1,428,000,000	(601,000,000)	2,861,000,000
Operating Segments | Corporate Segment
Segment reporting information
Operating expenses			234,000,000		455,000,000
Operating profit (loss)	(263,000,000)		(234,000,000)	(527,000,000)	(455,000,000)
Intersegment Eliminations
Segment reporting information
Net revenues	(7,211,000,000)		(6,194,000,000)	(14,168,000,000)	(12,244,000,000)
Cost of revenue			(5,985,000,000)		(11,843,000,000)
Gross profit	(206,000,000)		(209,000,000)	(401,000,000)	(401,000,000)
Operating expenses			(20,000,000)		(36,000,000)
Operating profit (loss)	(187,000,000)		(189,000,000)	(362,000,000)	(365,000,000)
Previously Reported
Segment reporting information
Cost of revenue			38,750,000,000		76,684,000,000
Gross profit			6,935,000,000		13,515,000,000
Operating expenses			4,818,000,000		9,605,000,000
Operating profit (loss)			2,117,000,000		3,910,000,000
Previously Reported | Operating Segments | Pharmacy Services Segment
Segment reporting information
Cost of revenue			30,856,000,000		60,983,000,000
Gross profit			1,469,000,000		2,565,000,000
Operating expenses			334,000,000		646,000,000
Operating profit (loss)			1,135,000,000		1,919,000,000
Previously Reported | Operating Segments | Retail/LTC Segment
Segment reporting information
Cost of revenue			13,879,000,000		27,544,000,000
Gross profit			5,675,000,000		11,351,000,000
Operating expenses			4,264,000,000		8,529,000,000
Operating profit (loss)			1,411,000,000		2,822,000,000
Previously Reported | Operating Segments | Corporate Segment
Segment reporting information
Operating expenses			240,000,000		466,000,000
Operating profit (loss)			(240,000,000)		(466,000,000)
Previously Reported | Intersegment Eliminations
Segment reporting information
Cost of revenue			(5,985,000,000)		(11,843,000,000)
Gross profit			(209,000,000)		(401,000,000)
Operating expenses			(20,000,000)		(36,000,000)
Operating profit (loss)			(189,000,000)		(365,000,000)
Adjustments.
Segment reporting information
Cost of revenue			9,000,000		18,000,000
Gross profit			(9,000,000)		(18,000,000)
Operating expenses			(9,000,000)		(18,000,000)
Adjustments. | Operating Segments | Pharmacy Services Segment
Segment reporting information
Cost of revenue			12,000,000		26,000,000
Gross profit			(12,000,000)		(26,000,000)
Operating expenses			11,000,000		24,000,000
Operating profit (loss)			(23,000,000)		(50,000,000)
Adjustments. | Operating Segments | Retail/LTC Segment
Segment reporting information
Cost of revenue			(3,000,000)		(8,000,000)
Gross profit			3,000,000		8,000,000
Operating expenses			(14,000,000)		(31,000,000)
Operating profit (loss)			17,000,000		39,000,000
Adjustments. | Operating Segments | Corporate Segment
Segment reporting information
Operating expenses			(6,000,000)		(11,000,000)
Operating profit (loss)			6,000,000		11,000,000
Omnicare, Inc. | Retail/LTC Segment | Gross Profit
Segment reporting information
Acquisition related costs			5,000,000		5,000,000
Omnicare, Inc. | Retail/LTC Segment | Operating profit
Segment reporting information
Integration related costs			$ 10,000,000	3,000,000	$ 25,000,000
Aetna Acquisition | Corporate Segment | Operating profit
Segment reporting information
Business Combination Acquisition Related Costs And Integration Related Costs	$ 39,000,000			$ 79,000,000