Financial Instruments (Carrying Value And Fair Value Of Convertible Senior Notes) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended				9 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2012		Dec. 31, 2012 0.75% Convertible Senior Notes Due 2016	Mar. 31, 2012 0.75% Convertible Senior Notes Due 2016
Financial Instruments
Marketable Securities, Realized Loss, Other than Temporary Impairments, Amount	$ 0	$ 0	$ 0	$ 0
Convertible Senior Notes, Carrying Value	554		554		539	[1]
Convertible Senior Notes, Fair Value							$ 583	$ 584
Interest rate percentage on convertible senior notes, due 2016	0.75%		0.75%		0.75%		0.75%	0.75%
Convertible Senior Notes, Maturity Date (Year)							2016	2016

[1] Derived from audited consolidated financial statements.