Goodwill Impairment Charges (Details) $ in Millions	3 Months Ended			9 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($) reporting_unit	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Goodwill [Line Items]
Pretax goodwill impairment charges	$ 2	$ 21		$ 2	$ 591
After-tax goodwill impairment					591
European Pharmaceutical Solutions
Goodwill [Line Items]
Pretax goodwill impairment charges				0	570
After-tax goodwill impairment			$ 570		$ 570
Number of reporting units | reporting_unit			2
European Pharmaceutical Solutions | Pharmaceutical Distributions Reporting Unit
Goodwill [Line Items]
Pretax goodwill impairment charges			$ 238
After-tax goodwill impairment			$ 238
Discount rate (percent)			8.00%
Terminal growth rate (percent)			1.25%
European Pharmaceutical Solutions | Retail Pharmacy Reporting Unit
Goodwill [Line Items]
Pretax goodwill impairment charges			$ 332
After-tax goodwill impairment			$ 332
Discount rate (percent)			8.50%
Terminal growth rate (percent)			1.25%
Other
Goodwill [Line Items]
Pretax goodwill impairment charges				$ 2
Other | Rexall Health
Goodwill [Line Items]
Pretax goodwill impairment charges		21
After-tax goodwill impairment		$ 21