Goodwill Impairment Charges (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Goodwill [Line Items]
Goodwill impairment charge	$ 0		$ 0		$ 350	$ 290
Goodwill	11,828				11,828		$ 10,586
Technology Solutions
Goodwill [Line Items]
Goodwill impairment charge					0
Goodwill	0				0		$ 454
Mckesson Europe Reporting Unit
Goodwill [Line Items]
Goodwill impairment charge		$ 350
Discount rate used (percent)		7.50%					7.00%
Terminal growth rate used (percent)		1.25%					1.50%
Goodwill	$ 2,692				$ 2,692
Enterprise Information Solutions | Technology Solutions
Goodwill [Line Items]
Goodwill impairment charge			$ 290	$ 290
Goodwill impairment charge, after tax				$ 282
McKesson Europe Plan
Goodwill [Line Items]
Goodwill impairment charge, after tax		$ 350