Derivative Instruments - Narrative (Details) - USD ($)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Oct. 31, 2018	May 31, 2018
Derivative [Line Items]
Cash flow hedge adjustment, net of tax	$ (44,000,000)	$ (23,000,000)
Reclassifications during period	11,000,000	8,000,000
Net losses reclassified to earnings, net of tax	8,000,000	6,000,000	$ 0
Interest rate swap
Derivative [Line Items]
Pre-tax impact of gain (loss) on derivatives	(59,000,000)	$ (31,000,000)
Designated as hedging instrument | Interest rate swap
Derivative [Line Items]
Foreign currency cash flow hedge gain to be reclassified during next 12 months	39,000,000
Designated as hedging instrument | Cash flow hedging | Interest rate swap
Derivative [Line Items]
Derivative notional amount	$ 1,600,000,000			$ 200,000,000	$ 1,400,000,000