Acquisitions 3 (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Business Combinations [Abstract]
Accrued acquisition-related costs related to purchase price amounts withheld subject to indemnification protections		$ 11		$ 11		$ 12
Business Acquisition
Purchase accounting adjustments for additional deferred tax assets	[1]			(99)
Total revenue		1,093	$ 1,007	3,152	$ 3,024
Net (loss) income		(93)	$ 208	269	$ 618
Veracode
Business Acquisition
Purchase accounting adjustments for additional deferred tax assets		(72)
Automic and Veracode
Business Acquisition
Total revenue		68		182
Net (loss) income		$ (16)		$ (53)

[1] Acquisitions amount relates to purchase price allocation adjustments that occurred during the nine months ended December 31, 2017.