Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified							1 Months Ended
	Sep. 30, 2014	Mar. 31, 2014		Sep. 30, 2013	Mar. 31, 2013	Jul. 14, 2011 Convertible Debt	Jul. 31, 2011 Convertible Debt	Jul. 14, 2011 Convertible Debt
Financial Instruments
Cash and Cash Equivalents, at Carrying Value	$ 1,624	$ 1,782	[1]	$ 1,090	$ 1,292
Contractual interest rate of 0.75% Convertible Senior Notes due 2016						0.75%		0.75%
Debt Instrument, Maturity Date, Description							2016

[1] Derived from audited consolidated financial statements.