Segment Information (Details) $ in Millions	3 Months Ended						9 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment							2
Revenues
Total Revenues	$ 53,617				$ 50,130		$ 156,729	$ 149,820
Operating profit
Total	834				831		1,706	2,383
Interest Expense	(67)				(74)		(204)	(231)
Income from Continuing Operations Before Income Taxes	697				780		1,333	2,217
Reversal of LIFO expense							5	151
Net restructuring charges recognized							9
Goodwill impairment charge	0				0		350	290
Loss from equity method investment in Change Healthcare	90				0		271	0
Gain from sale of business, pre-tax	109				0		109	0
Mckesson Europe Reporting Unit
Operating profit
Goodwill impairment charge		$ 350
Total Distribution Solutions
Operating profit
Pre-tax gain recorded on sale of investment							43
Goodwill impairment charge							350
Technology Solutions
Operating profit
Goodwill impairment charge							0
Technology Solutions | Enterprise Information Solutions
Operating profit
Goodwill impairment charge					290	$ 290
Operating Segments
Revenues
Total Revenues	53,617				50,130		156,729	149,820
Operating profit
Total	884				945		1,874	2,718
Operating Segments | Total Distribution Solutions
Revenues
Total Revenues	53,617				49,436		156,489	147,722
Operating profit
Total	$ 819				$ 813		$ 1,920	$ 2,592
Revenue derived from services, percentage (less than)	2.00%				2.00%		2.00%	2.00%
Proceeds from legal settlements								$ 144
Operating Segments | Total Distribution Solutions | LIFO Method of Accounting
Operating profit
Total	$ 2				$ 155		$ 5	151
Operating Segments | Total Distribution Solutions | Reportable Subsegments | North America pharmaceutical distribution and services
Revenues
Total Revenues	44,935				41,685		131,459	124,271
Operating Segments | Total Distribution Solutions | Reportable Subsegments | International pharmaceutical distribution and services
Revenues
Total Revenues	6,989				6,193		20,144	18,794
Operating Segments | Total Distribution Solutions | Reportable Subsegments | Medical-Surgical distribution and services
Revenues
Total Revenues	1,693				1,558		4,886	4,657
Operating Segments | Technology Solutions
Revenues
Total Revenues	0				694		240	2,098
Operating profit
Total	65				132		(46)	126
Corporate
Operating profit
Corporate Expenses, Net	(120)				$ (91)		(337)	$ (270)
Net restructuring charges recognized							2
Joint Venture | Change Healthcare, LLC (“Change Healthcare”)
Operating profit
Loss from equity method investment in Change Healthcare	90						271
Core MTS Businesses | Change Healthcare, LLC (“Change Healthcare”) | Operating Segments | Technology Solutions
Operating profit
Gain from sale of business, pre-tax			$ 37	$ 3,947
Change Healthcare, LLC (“Change Healthcare”) | Tax Receivable Agreement (“TRA”)
Operating profit
Reduction in TRA liability	46						46
McKesson Europe Plan
Operating profit
Net restructuring charges recognized							592
Intangible Asset and Store Assets Impairment | McKesson Europe Plan
Operating profit
Net restructuring charges recognized		$ 189
Held-for-sale | Enterprise Information Solutions
Operating profit
Gain from sale of business, pre-tax	$ 109						$ 109