Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ (19)	$ (16)	$ 2
Other comprehensive income (loss) before reclassifications	(107)	34	(6)
Amounts reclassified from accumulated other comprehensive income (loss)	(1)	(37)	(12)
Net current-period other comprehensive income (loss)	(108)	(3)	(18)
Ending balance	(127)	(19)	(16)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(3)	1	(3)
Other comprehensive income (loss) before reclassifications	(9)	(3)	4
Amounts reclassified from accumulated other comprehensive income (loss)	4	(1)	0
Net current-period other comprehensive income (loss)	(5)	(4)	4
Ending balance	(8)	(3)	1
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	32	14	21
Other comprehensive income (loss) before reclassifications	(126)	54	5
Amounts reclassified from accumulated other comprehensive income (loss)	5	(36)	(12)
Net current-period other comprehensive income (loss)	(121)	18	(7)
Ending balance	(89)	32	14
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(48)	(31)	(16)
Other comprehensive income (loss) before reclassifications	28	(17)	(15)
Amounts reclassified from accumulated other comprehensive income (loss)	(10)	0	0
Net current-period other comprehensive income (loss)	18	(17)	(15)
Ending balance	(30)	(48)	(31)
Interest Income [Member] | Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amounts reclassified from accumulated other comprehensive income (loss)	4	(1)	0
Interest Income [Member] | Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amounts reclassified from accumulated other comprehensive income (loss)	$ (10)	$ 0	$ 0