Fair Value Measurements (Details) - USD ($)	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount of liabilities	$ 8,015,000,000		$ 8,015,000,000		$ 8,362,000,000
Pre-tax charges recorded during period	236,000,000	$ 0	236,000,000	$ 0
Goodwill impairment charge	350,000,000	290,000,000	350,000,000	$ 290,000,000
McKesson Europe Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pre-tax charges recorded during period	586,000,000
Goodwill impairment charge	350,000,000
Goodwill impairment charge, after tax	350,000,000
Technology Solutions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill impairment charge			0
Technology Solutions | Enterprise Information Solutions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill impairment charge		290,000,000
Goodwill impairment charge, after tax		$ 282,000,000
Fair malue, measurements, recurring | Fair value, inputs, level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair values of liabilities	8,500,000,000		8,500,000,000		8,700,000,000
Fair malue, measurements, recurring | Fair value, inputs, level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in money market funds	279,000,000		$ 279,000,000		478,000,000
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value on a nonrecurring basis					$ 0
Intangible Asset and Store Assets Impairment | McKesson Europe Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pre-tax charges recorded during period	189,000,000
After-tax charges recorded	$ 157,000,000