Changes in Accumulated Other Comprehensive Income by Component (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 56		$ 69	[1]
Other comprehensive income (loss) before reclassifications	6		(9)
Amounts reclassified from accumulated other comprehensive income	0		2
Net current-period other comprehensive income (loss)	6	34	(7)		(24)
Ending balance	62		62
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(5)		(4)
Other comprehensive income (loss) before reclassifications	1		0
Amounts reclassified from accumulated other comprehensive income	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	0		0
Other comprehensive income (loss) before reclassifications	(9)		(11)
Amounts reclassified from accumulated other comprehensive income	0		2
Net current-period other comprehensive income (loss)	(9)		(9)
Ending balance	(9)		(9)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	61		73
Other comprehensive income (loss) before reclassifications	14		2
Amounts reclassified from accumulated other comprehensive income	0		0
Net current-period other comprehensive income (loss)	14		2
Ending balance	$ 75		$ 75

[1] Derived from audited consolidated financial statements.