Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 3	$ (14)	$ (16)	$ 2
Other comprehensive income (loss) before reclassifications	(8)	(25)	17	(38)
Amounts reclassified from accumulated other comprehensive income (loss)	(5)	(5)	(11)	(8)
Total other comprehensive income (loss), net of tax	(13)	(30)	6	(46)
Ending balance	(10)	(44)	(10)	(44)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	3	(4)	1	(3)
Other comprehensive income (loss) before reclassifications	(1)	2	1	1
Amounts reclassified from accumulated other comprehensive income (loss)	(1)	(1)	(1)	(1)
Total other comprehensive income (loss), net of tax	(2)	1	0	0
Ending balance	1	(3)	1	(3)
Unrealized Gains (Losses) on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	36	5	14	21
Other comprehensive income (loss) before reclassifications	(1)	5	27	(8)
Amounts reclassified from accumulated other comprehensive income (loss)	(4)	(4)	(10)	(7)
Total other comprehensive income (loss), net of tax	(5)	1	17	(15)
Ending balance	31	6	31	6
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(36)	(15)	(31)	(16)
Other comprehensive income (loss) before reclassifications	(6)	(32)	(11)	(31)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0	0
Total other comprehensive income (loss), net of tax	(6)	(32)	(11)	(31)
Ending balance	$ (42)	$ (47)	$ (42)	$ (47)