Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified						6 Months Ended
	Sep. 30, 2013	Mar. 31, 2013		Sep. 30, 2012	Mar. 31, 2012	Sep. 30, 2013 0.75% Convertible Senior Notes Due 2016
Financial Instruments
Cash and Cash Equivalents, at Carrying Value	$ 1,090	$ 1,292	[1]	$ 871	$ 1,293
Contractual interest rate of 0.75% Convertible Senior Notes due 2016	0.75%	0.75%				0.75%
Debt Instrument Maturity Year						2016

[1] Derived from audited consolidated financial statements.