Goodwill Impairment Charges (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Goodwill [Line Items]
Non-cash pre-tax charge			$ 1,738,000,000	$ 290,000,000	$ 0
Goodwill	$ 10,924,000,000		10,924,000,000	10,586,000,000	9,786,000,000
Mckesson Europe Reporting Unit
Goodwill [Line Items]
Non-cash pre-tax charge			1,283,000,000
Distribution Solutions
Goodwill [Line Items]
Non-cash pre-tax charge			1,738,000,000	0
Goodwill	10,924,000,000		10,924,000,000	$ 10,132,000,000	7,987,000,000
Distribution Solutions | Mckesson Europe Reporting Unit
Goodwill [Line Items]
Non-cash pre-tax charge	933,000,000	$ 350,000,000
Goodwill	$ 1,851,000,000		1,851,000,000
Goodwill impairment, discount rate (percent)	8.00%	7.50%		7.00%
Goodwill impairment, terminal growth rate (percent)	1.25%	1.25%		1.50%
Distribution Solutions | Rexall Health
Goodwill [Line Items]
Non-cash pre-tax charge	$ 455,000,000		455,000,000
Goodwill	0		$ 0
Goodwill impairment, discount rate (percent)			10.00%
Goodwill impairment, terminal growth rate (percent)			2.00%
Technology Solutions
Goodwill [Line Items]
Non-cash pre-tax charge			$ 0	$ 290,000,000
Non-cash after-tax charge				282,000,000
Goodwill	$ 0		$ 0	$ 454,000,000	$ 1,799,000,000