Valuation and Qualifying Accounts (Details) - Allowance for Doubtful Accounts - USD ($) $ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period		$ 11	$ 9	$ 17
Additions/(deductions) charged/(credited) to costs and expenses		2	3	(2)
Deductions	[1]	(3)	(1)	(6)
Balance at end of period		$ 10	$ 11	$ 9

[1] Write-off of amounts against allowance provided.