Segments of Business (Details) $ in Millions, $ in Millions			3 Months Ended					6 Months Ended		9 Months Ended
	May 23, 2018 USD ($)	May 23, 2018 CAD ($)	Sep. 30, 2018 USD ($) country	Jun. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) segment country	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 CAD ($)
Revenues
Total Revenues			$ 53,075		$ 52,061			$ 105,682	$ 103,112
Operating profit
Total operating profit			689		239			772	872
Corporate Expenses, Net (6)			(167)		(108)			(290)	(217)
Interest Expense			(66)		(69)			(127)	(137)
Income from Continuing Operations Before Income Taxes			587		178			$ 593	636
Number of reportable segments | segment								3
Pre-tax credits related to LIFO accounting								$ 43	3
Goodwill and asset impairment charges			0	$ 570	350			570	350
Pre-tax restructuring and asset impairment charges			82		236			178	236
After-tax restructuring and asset impairment charges			67		197			152
Loss from equity method investment in Change Healthcare			56		61			112	181
U.S. Pharmaceutical and Specialty Solutions
Operating profit
Pre-tax credits related to LIFO accounting			$ 22		29			43	3
Goodwill and asset impairment charges								$ 0
European Pharmaceutical Solutions
Operating profit
Number of countries in which entity segment operates | country			13					13
Goodwill and asset impairment charges				$ 570				$ 570
Medical-Surgical Solutions
Operating profit
Goodwill and asset impairment charges								0
Other
Operating profit
Goodwill and asset impairment charges								0
Operating Segments
Revenues
Total Revenues			$ 53,075		52,061			105,682	103,112
Operating profit
Total operating profit			$ 820		$ 355			$ 1,010	$ 990
Revenue derived from services, percentage (less than)			1.00%		1.00%			1.00%	1.00%
Operating Segments | U.S. Pharmaceutical and Specialty Solutions
Revenues
Total Revenues			$ 41,610		$ 40,603			$ 82,587	$ 80,885
Operating profit
Total operating profit			610		710			1,153	1,185
Proceeds from legal settlements								(35)
Operating Segments | European Pharmaceutical Solutions
Revenues
Total Revenues			6,639		6,773			13,574	13,155
Operating profit
Total operating profit			$ 10		$ (547)			$ (550)	$ (512)
Revenue derived from services, percentage (less than)			10.00%		10.00%			10.00%	10.00%
Goodwill and asset impairment charges					$ 236			$ 570
Pre-tax restructuring and asset impairment charges									$ 236
After-tax restructuring and asset impairment charges									197
After-tax goodwill impairment								570
Operating Segments | Medical-Surgical Solutions
Revenues
Total Revenues			$ 1,948		1,660			3,651	3,193
Operating profit
Total operating profit			$ 105		$ 118			$ 198	$ 226
Revenue derived from services, percentage (less than)			1.00%		1.00%			1.00%	1.00%
Operating Segments | Other
Revenues
Total Revenues			$ 2,878		$ 3,025			$ 5,870	$ 5,879
Operating profit
Total operating profit			95		74			209	91
Joint Venture | Change Healthcare, LLC (“Change Healthcare”)
Operating profit
Ownership interest in the joint venture (percent)							70.00%
Loss from equity method investment in Change Healthcare			$ 56		61			$ 112	181
Core MTS Businesses | Change Healthcare, LLC (“Change Healthcare”) | Operating Segments | Other
Operating profit
Gain from sale of business, pre-tax						$ 37	$ 3,947
Gain from sale of business, after tax						$ 22	$ 3,018
Core MTS Businesses | Joint Venture
Operating profit
Ownership interest in the joint venture (percent)			70.00%					70.00%
United States
Revenues
Total Revenues			$ 43,774		42,558			$ 86,664	84,669
Foreign
Revenues
Total Revenues			9,301		9,503			19,018	18,443
Third Party Seller of Rexall Health | Rexall Health | CANADA
Operating profit
Net restructuring charges recognized								97
Proceeds from prior acquisitions	$ 97	$ 125								$ 119	$ 147
Strategic Growth Initiative Plan
Operating profit
Net restructuring charges recognized			53					111
Strategic Growth Initiative Plan | U.S. Pharmaceutical and Specialty Solutions
Operating profit
Net restructuring charges recognized			5					13
Strategic Growth Initiative Plan | Medical-Surgical Solutions
Operating profit
Net restructuring charges recognized			6					18
Strategic Growth Initiative Plan | Other
Operating profit
Net restructuring charges recognized			42					80
Net restructuring charges recognized, after tax			37					76
Mckesson Europe Reporting Unit | Operating Segments | European Pharmaceutical Solutions
Operating profit
Goodwill and asset impairment charges					350				350
After-tax goodwill impairment					$ 350				$ 350
Tax Receivable Agreement (“TRA”) | Change Healthcare, LLC (“Change Healthcare”) | Other
Operating profit
Gain on derecognition of liability, pre-tax			90
Gain on derecognition of liability, after tax			66
Opioid-Related Case
Operating profit
Litigation expenses and other-related costs			43					59
Litigation expenses and other-related costs, after tax			$ 32					$ 48