Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2015		Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 2	[1]	$ 37
Other comprehensive income (loss) before reclassifications	(13)		19
Amounts reclassified from accumulated other comprehensive income (loss)	(3)		5
Net current-period other comprehensive income (loss)	(16)		24
Ending balance	(14)		61
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(3)		(4)
Other comprehensive income (loss) before reclassifications	(1)		0
Amounts reclassified from accumulated other comprehensive income (loss)	0		0
Net current-period other comprehensive income (loss)	(1)		0
Ending balance	(4)		(4)
Unrealized Gains (Losses) on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	21		(10)
Other comprehensive income (loss) before reclassifications	(13)		(1)
Amounts reclassified from accumulated other comprehensive income (loss)	(3)		5
Net current-period other comprehensive income (loss)	(16)		4
Ending balance	5		(6)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(16)		51
Other comprehensive income (loss) before reclassifications	1		20
Amounts reclassified from accumulated other comprehensive income (loss)	0		0
Net current-period other comprehensive income (loss)	1		20
Ending balance	$ (15)		$ 71

[1] Derived from audited consolidated financial statements.