Acquisitions - Fiscal 2019 Acquisitions (Details) $ in Millions		12 Months Ended
	Oct. 01, 2018 USD ($)	Mar. 31, 2019 USD ($) acquisition	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Business Acquisition [Line Items]
Goodwill		$ 7,606	$ 7,619	$ 1,855
Molina Medicaid Solutions
Business Acquisition [Line Items]
Total consideration transferred	$ 233
Current assets acquired	91
Intangible assets, other than goodwill	112
Other assets(2)	11
Current liabilities	50
Other liabilities	22
Goodwill	$ 91
Useful lives (years)	13 years
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Total consideration transferred		228
Current assets acquired		73
Intangible assets, other than goodwill		71
Other assets(2)		10
Current liabilities		63
Goodwill		$ 137
Number of businesses acquired | acquisition		7
Payments to acquire businesses		$ 187
Contingent consideration		$ 41