Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ (10)	$ (44)	$ (16)	$ 2
Other comprehensive income (loss) before reclassifications	17	(10)	34	(48)
Amounts reclassified from accumulated other comprehensive income (loss)	(8)	(3)	(19)	(11)
Total other comprehensive income (loss), net of tax	9	(13)	15	(59)
Ending balance	(1)	(57)	(1)	(57)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1	(3)	1	(3)
Other comprehensive income (loss) before reclassifications	(5)	(4)	(4)	(3)
Amounts reclassified from accumulated other comprehensive income (loss)	0	1	(1)	0
Total other comprehensive income (loss), net of tax	(5)	(3)	(5)	(3)
Ending balance	(4)	(6)	(4)	(6)
Unrealized Gains (Losses) on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	31	6	14	21
Other comprehensive income (loss) before reclassifications	39	10	66	2
Amounts reclassified from accumulated other comprehensive income (loss)	(8)	(4)	(18)	(11)
Total other comprehensive income (loss), net of tax	31	6	48	(9)
Ending balance	62	12	62	12
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(42)	(47)	(31)	(16)
Other comprehensive income (loss) before reclassifications	(17)	(16)	(28)	(47)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0	0
Total other comprehensive income (loss), net of tax	(17)	(16)	(28)	(47)
Ending balance	$ (59)	$ (63)	$ (59)	$ (63)