Sale of Receivables (Details)	3 Months Ended		6 Months Ended
	Sep. 30, 2019 USD ($) extension	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) extension	Sep. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)
Receivables [Abstract]
Receivables facility, amount	$ 750,000,000		$ 750,000,000		$ 600,000,000
Availability under receivable facility	663,000,000		663,000,000
Drawn amount	$ 650,000,000		$ 650,000,000
Number of extensions | extension	1		1
Extension term			1 year
Gain (loss) on sale of receivables			$ 0
Transfer of Financial Assets Accounted for as Sales, Deferred Purchase Price [Roll Forward]
Deferred purchase price receivable, Beginning balance	$ 525,000,000	$ 207,000,000	574,000,000	$ 233,000,000
Transfers of receivables	0	2,436,000,000	1,214,000,000	2,976,000,000
Collections	0	(1,378,000,000)	(1,265,000,000)	(1,900,000,000)
Change in funding availability	0	(295,000,000)	2,000,000	(310,000,000)
Facility amendments	(525,000,000)	(457,000,000)	(525,000,000)	(457,000,000)
Fair value adjustment	0	27,000,000	0	(2,000,000)
Deferred purchase price receivable, Ending balance	$ 0	$ 540,000,000	$ 0	540,000,000
Transfers of receivables				464,000,000
Collections				521,000,000
Operating cash flow effect				$ (57,000,000)