Stockholders' Equity (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) $ in Millions	6 Months Ended
	Sep. 30, 2016 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
April 1, 2016	$ 3,676	[1]
September 30, 2016	3,862
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
April 1, 2016	15
Other comprehensive loss before reclassifications	(22)
September 30, 2016	(7)
Unrealized Gain on Available-For-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
April 1, 2016	7
Other comprehensive loss before reclassifications	(1)
September 30, 2016	6
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
April 1, 2016	22
Other comprehensive loss before reclassifications	(23)
September 30, 2016	$ (1)

[1] Derived from audited financial statements.