Stockholders' Equity (Schedule of Accumulated Other Comprehensive Income) (Details) $ in Millions	12 Months Ended
	Mar. 31, 2017 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of April 1, 2016	$ 3,676
Balance as of March 31, 2017	3,487
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of April 1, 2016	15
Other comprehensive loss before reclassifications	(8)
Balance as of March 31, 2017	7
Unrealized Gain On Available-For-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of April 1, 2016	7
Other comprehensive loss before reclassifications	(2)
Balance as of March 31, 2017	5
Total AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of April 1, 2016	22
Other comprehensive loss before reclassifications	(10)
Balance as of March 31, 2017	$ 12