Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2012		Mar. 31, 2011
Financial Instruments
Proceeds from Sale of Investment Projects	$ 46	$ 25
Gain on Sale of Investments	25	14
Cash and Cash Equivalents, at Carrying Value		1,158	1,242	1,158	1,242	1,293	[1]	1,579
Contractual interest rate of 0.75% Convertible Senior Notes due 2016		0.75%		0.75%		0.75%
Impairment charges on marketable equity securities		$ 0	$ 0	$ 0	$ 0
0.75% Convertible Senior Notes Due 2016
Financial Instruments
Contractual interest rate of 0.75% Convertible Senior Notes due 2016		0.75%		0.75%		0.75%

[1] Derived from audited consolidated financial statements.