Goodwill Impairment Charges (Details)	3 Months Ended					12 Months Ended
	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016	Mar. 31, 2019 USD ($) reporting_unit	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Goodwill [Line Items]
Non-cash pre-tax charge						$ 1,797,000,000	$ 1,738,000,000	$ 290,000,000
Non-cash after-tax charge							1,738,000,000
Goodwill	$ 9,358,000,000		$ 10,924,000,000			9,358,000,000	10,924,000,000	10,586,000,000
European Pharmaceutical Solutions
Goodwill [Line Items]
Non-cash pre-tax charge	1,206,000,000	$ 570,000,000				1,776,000,000	1,283,000,000
Non-cash after-tax charge						$ 1,756,000,000	1,283,000,000
Number of Reporting Units | reporting_unit						2
Goodwill	0		1,850,000,000			$ 0	1,850,000,000	2,789,000,000
Other
Goodwill [Line Items]
Non-cash pre-tax charge						21,000,000	455,000,000	290,000,000
Goodwill	2,829,000,000		2,894,000,000			2,829,000,000	2,894,000,000	2,337,000,000
Technology Solutions
Goodwill [Line Items]
Non-cash pre-tax charge								290,000,000
Non-cash after-tax charge								$ 282,000,000
Rexall Health
Goodwill [Line Items]
Non-cash pre-tax charge			455,000,000
Rexall Health | Other
Goodwill [Line Items]
Non-cash pre-tax charge							455,000,000
Non-cash after-tax charge							$ 455,000,000
Goodwill impairment, discount rate (percent)							10.00%
Goodwill impairment, terminal growth rate (percent)							2.00%
Goodwill	0		0			0	$ 0
Pharmacy Solutions Reporting Unit | European Pharmaceutical Solutions
Goodwill [Line Items]
Non-cash pre-tax charge	741,000,000	238,000,000
Non-cash after-tax charge	$ 741,000,000	$ 238,000,000
Goodwill impairment, discount rate (percent)	9.00%	8.00%
Goodwill impairment, terminal growth rate (percent)	1.25%	1.25%
Goodwill	$ 0					0
Consumer Solutions Reporting Unit | European Pharmaceutical Solutions
Goodwill [Line Items]
Non-cash pre-tax charge	465,000,000	$ 332,000,000
Non-cash after-tax charge	$ 445,000,000	$ 332,000,000
Goodwill impairment, discount rate (percent)	10.00%	8.50%
Goodwill impairment, terminal growth rate (percent)	1.25%	1.25%
Goodwill	$ 0					$ 0
Mckesson Europe Reporting Unit | European Pharmaceutical Solutions
Goodwill [Line Items]
Non-cash pre-tax charge			933,000,000	$ 350,000,000
Non-cash after-tax charge				$ 350,000,000
Goodwill impairment, discount rate (percent)				7.50%	7.00%		8.00%
Goodwill impairment, terminal growth rate (percent)				1.25%	1.50%		1.25%
Mckesson Europe Reporting Unit | Other
Goodwill [Line Items]
Non-cash after-tax charge			$ 933,000,000