Changes in Accumulated Other Comprehensive Income by Component (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 37	$ 69	$ 173
Other comprehensive income (loss) before reclassifications	(46)	(41)	(67)
Amounts reclassified from accumulated other comprehensive income	11	9	(37)
Net current-period other comprehensive income (loss)	(35)	(32)	(104)
Ending balance	2	37	69
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(4)	(4)	83
Other comprehensive income (loss) before reclassifications	1	0	(46)
Amounts reclassified from accumulated other comprehensive income	0	0	(41)
Net current-period other comprehensive income (loss)	1	0	(87)
Ending balance	(3)	(4)	(4)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(10)	0	(2)
Other comprehensive income (loss) before reclassifications	20	(19)	(2)
Amounts reclassified from accumulated other comprehensive income	11	9	4
Net current-period other comprehensive income (loss)	31	(10)	2
Ending balance	21	(10)	0
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	51	73	92
Other comprehensive income (loss) before reclassifications	(67)	(22)	(19)
Amounts reclassified from accumulated other comprehensive income	0	0	0
Net current-period other comprehensive income (loss)	(67)	(22)	(19)
Ending balance	$ (16)	$ 51	$ 73