Segments of Business (Details) $ in Millions, $ in Millions			3 Months Ended						6 Months Ended		9 Months Ended
	May 23, 2018 USD ($)	May 23, 2018 CAD ($)	Dec. 31, 2018 USD ($) country	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 CAD ($)	Dec. 31, 2018 USD ($) segment country	Dec. 31, 2017 USD ($)
Revenues
Total Revenues			$ 56,208			$ 53,617					$ 161,890	$ 156,729
Operating profit (8)
Total operating profit			683			834					1,455	1,706
Corporate Expenses, Net			(190)			(120)					(480)	(337)
Interest Expense			(67)			(67)					(194)	(204)
Income from Continuing Operations Before Income Taxes			650			697					$ 1,243	1,333
Number of reportable segments | segment											3
Pre-tax credits related to LIFO accounting											$ 64	5
Proceeds from legal settlements			104								139
Pretax charge related to customer bankruptcy			60								60
Pretax goodwill impairment charges			21			0					591	350
Goodwill and other asset impairment charges											671	539
Pre-tax restructuring and asset impairment charges			110			6					288	242
After-tax restructuring and asset impairment charges			92			5					244	202
Gain from sale of business, pre-tax			0			109					0	109
Net income (loss) from Change Healthcare			(50)			(90)					$ (162)	(271)
U.S. Pharmaceutical and Specialty Solutions
Operating profit (8)
Revenue derived from services, percentage (less than)											1.00%
Pre-tax credits related to LIFO accounting			$ 21			2					$ 64	5
Pre-tax gain on sale of equity method investments						43						43
After-tax gain on sale of equity method investments						26						26
Pretax goodwill impairment charges											$ 0
European Pharmaceutical Solutions
Operating profit (8)
Number of countries in which entity segment operates | country			13								13
Revenue derived from services, percentage (less than)											10.00%
Pretax goodwill impairment charges					$ 570						$ 570
After-tax goodwill impairment					$ 570
Medical-Surgical Solutions
Operating profit (8)
Revenue derived from services, percentage (less than)											1.00%
Pretax goodwill impairment charges											$ 0
Other
Operating profit (8)
Pre-tax gain on sale of equity method investments			$ 56								56
After-tax gain on sale of equity method investments			41								41
Pretax goodwill impairment charges											21
Operating Segments
Revenues
Total Revenues			56,208			53,617					161,890	156,729
Operating profit (8)
Total operating profit			$ 907			$ 884					1,917	$ 1,874
Revenue derived from services, percentage (less than)			1.00%			1.00%						1.00%
Operating Segments | U.S. Pharmaceutical and Specialty Solutions
Revenues
Total Revenues			$ 44,279			$ 41,969					126,866	$ 122,854
Operating profit (8)
Total operating profit			671			565					1,824	1,750
Operating Segments | European Pharmaceutical Solutions
Revenues
Total Revenues			6,911			6,989					20,485	20,144
Operating profit (8)
Total operating profit			$ 26			$ 16					(524)	$ (496)
Revenue derived from services, percentage (less than)			10.00%			10.00%						10.00%
Pretax goodwill impairment charges											570
After-tax goodwill impairment											570
Pre-tax restructuring and asset impairment charges												$ 242
After-tax restructuring and asset impairment charges												202
Operating Segments | Medical-Surgical Solutions
Revenues
Total Revenues			$ 2,012			$ 1,693					5,663	4,886
Operating profit (8)
Total operating profit			$ 136			$ 123					334	$ 349
Revenue derived from services, percentage (less than)			1.00%			1.00%						1.00%
Operating Segments | Other
Revenues
Total Revenues			$ 3,006			$ 2,966					8,876	$ 8,845
Operating profit (8)
Total operating profit			74			180					283	271
Gain (credit) on derecognition of liability, pre-tax						(46)						(46)
Gain (credit) on derecognition of liability, after tax						(30)						(30)
Joint Venture | Change Healthcare, LLC (“Change Healthcare”)
Operating profit (8)
Ownership interest in the joint venture (percent)								70.00%
Gain (credit) on derecognition of liability, pre-tax											90
Gain (credit) on derecognition of liability, after tax											66
Net income (loss) from Change Healthcare			$ (50)			(90)					$ (162)	(271)
Core MTS Businesses | Change Healthcare, LLC (“Change Healthcare”) | Operating Segments | Other
Operating profit (8)
Pre-tax gain on sale of equity method investments												37
After-tax gain on sale of equity method investments												22
Gain from sale of business, pre-tax							$ 37	$ 3,900
Gain from sale of business, after tax							$ 22	$ 3,000
Core MTS Businesses | Joint Venture
Operating profit (8)
Ownership interest in the joint venture (percent)			70.00%								70.00%
Enterprise Information Solutions
Operating profit (8)
Gain from sale of business, pre-tax						109
Gain from sale of business, after tax						30
Enterprise Information Solutions | Operating Segments | Other
Operating profit (8)
Gain from sale of business, pre-tax						109						109
Gain from sale of business, after tax						30						30
CANADA | Other
Operating profit (8)
Net restructuring charges recognized											$ 89
Net restructuring charges recognized, after tax											83
United States
Revenues
Total Revenues			$ 46,523			43,849					133,186	128,517
Foreign
Revenues
Total Revenues			9,685			$ 9,768					28,704	28,212
Third Party Seller of Rexall Health | Rexall Health | CANADA
Operating profit (8)
Proceeds from prior acquisitions	$ 97	$ 125							$ 119	$ 147	97
Strategic Growth Initiative Plan
Operating profit (8)
Net restructuring charges recognized			50								161
Strategic Growth Initiative Plan | Operating Segments | U.S. Pharmaceutical and Specialty Solutions
Operating profit (8)
Net restructuring charges recognized			4								17
Strategic Growth Initiative Plan | Operating Segments | Medical-Surgical Solutions
Operating profit (8)
Net restructuring charges recognized			6								24
Strategic Growth Initiative Plan | Operating Segments | Other
Operating profit (8)
Net restructuring charges recognized			9								89
Mckesson Europe Reporting Unit | Operating Segments | European Pharmaceutical Solutions
Operating profit (8)
Pretax goodwill impairment charges												350
After-tax goodwill impairment												$ 350
Rexall Health
Operating profit (8)
Goodwill and other asset impairment charges			35
Rexall Health | Other
Operating profit (8)
Pretax goodwill impairment charges			21
Goodwill and other asset impairment charges			56								56
Impairment of Goodwill and other long-lived assets, net of tax			56								56
After-tax goodwill impairment			21
Tax Receivable Agreement (“TRA”) | Change Healthcare, LLC (“Change Healthcare”) | Other
Operating profit (8)
Gain (credit) on derecognition of liability, pre-tax				$ 90
Gain (credit) on derecognition of liability, after tax				$ 66
Severance | Strategic Growth Initiative Plan - Relocation of Corporate Headquarters
Operating profit (8)
Net restructuring charges recognized			31								31
Net restructuring charges recognized, after tax			$ 23								$ 23