Goodwill Impairment Charges (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Goodwill [Line Items]
Goodwill impairment charge	$ 350	$ 290	$ 350	$ 290
Goodwill	11,732		11,732		$ 10,586
Technology Solutions
Goodwill [Line Items]
Goodwill impairment charge			0
Goodwill	$ 0		0		$ 454
Mckesson Europe Reporting Unit
Goodwill [Line Items]
Discount rate used (percent)	7.50%				7.00%
Terminal growth rate used (percent)	1.25%				1.50%
Goodwill	$ 2,689		$ 2,689
Enterprise Information Solutions | Technology Solutions
Goodwill [Line Items]
Goodwill impairment charge		290
Goodwill impairment charge, after tax		$ 282
McKesson Europe Plan
Goodwill [Line Items]
Goodwill impairment charge	350
Goodwill impairment charge, after tax	$ 350