Goodwill and Intangible Assets, Net - Goodwill Impairment Inputs (Details) - USD ($) $ in Millions	3 Months Ended					9 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Goodwill [Line Items]
Goodwill impairment charge							$ 2	$ 1,797	$ 1,738
Mckesson Europe and Rexall
Goodwill [Line Items]
Goodwill impairment charge						$ 1,738
European Pharmaceutical Solutions
Goodwill [Line Items]
Goodwill impairment charge	$ 1,200		$ 570				0	1,776	$ 1,300
European Pharmaceutical Solutions | PD
Goodwill [Line Items]
Goodwill impairment, discount rate (percent)			8.00%
Goodwill impairment, terminal growth rate (percent)			1.25%
Goodwill impairment charge			$ 238
European Pharmaceutical Solutions | RP
Goodwill [Line Items]
Goodwill impairment, discount rate (percent)	10.00%		8.50%
Goodwill impairment, terminal growth rate (percent)	1.25%		1.25%
Goodwill impairment charge	$ 465		$ 251
European Pharmaceutical Solutions | PD
Goodwill [Line Items]
Goodwill impairment, discount rate (percent)			8.00%
Goodwill impairment, terminal growth rate (percent)			1.25%
Goodwill impairment charge			$ 81
European Pharmaceutical Solutions | PD
Goodwill [Line Items]
Goodwill impairment, discount rate (percent)	9.00%
Goodwill impairment, terminal growth rate (percent)	1.25%
Goodwill impairment charge	$ 741
European Pharmaceutical Solutions | Mckesson Europe Reporting Unit
Goodwill [Line Items]
Goodwill impairment, discount rate (percent)				8.00%	7.50%
Goodwill impairment, terminal growth rate (percent)				1.25%	1.25%
Goodwill impairment charge				$ 933	$ 350
Other
Goodwill [Line Items]
Goodwill impairment charge							$ 2	$ 21
Other | Rexall Health
Goodwill [Line Items]
Goodwill impairment, discount rate (percent)				10.00%
Goodwill impairment, terminal growth rate (percent)				2.00%
Goodwill impairment charge		$ 21		$ 455