Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ (16)	$ 2	$ 37
Other comprehensive income (loss) before reclassifications	34	(6)	(46)
Amounts reclassified from accumulated other comprehensive income (loss)	(37)	(12)	11
Net current-period other comprehensive income (loss)	(3)	(18)	(35)
Ending balance	(19)	(16)	2
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	1	(3)	(4)
Other comprehensive income (loss) before reclassifications	(3)	4	1
Amounts reclassified from accumulated other comprehensive income (loss)	(1)	0	0
Net current-period other comprehensive income (loss)	(4)	4	1
Ending balance	(3)	1	(3)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	14	21	(10)
Other comprehensive income (loss) before reclassifications	54	5	20
Amounts reclassified from accumulated other comprehensive income (loss)	(36)	(12)	11
Net current-period other comprehensive income (loss)	18	(7)	31
Ending balance	32	14	21
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(31)	(16)	51
Other comprehensive income (loss) before reclassifications	(17)	(15)	(67)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0
Net current-period other comprehensive income (loss)	(17)	(15)	(67)
Ending balance	$ (48)	$ (31)	$ (16)