Derivative Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Cash Flow Hedging	Mar. 31, 2012 Cash Flow Hedging	Dec. 31, 2012 Balance Sheet Hedging	Mar. 31, 2012 Balance Sheet Hedging	Dec. 31, 2012 Nondesignated British Pounds Sterling Balance Sheet Hedging	Mar. 31, 2012 Nondesignated British Pounds Sterling Balance Sheet Hedging	Dec. 31, 2012 Nondesignated United States Dollar Balance Sheet Hedging	Mar. 31, 2012 Nondesignated United States Dollar Balance Sheet Hedging
Derivative
Maturity period, maximum (in months)	12 months
Notional value of foreign currency purchase contracts		$ 86	$ 74					$ 26	$ 37
Notional value of foreign currency sale contracts		179	78			8	8	489	197
Foreign currency option contracts outstanding		2	2
Notional value of foreign currency forward contracts				$ 523	$ 242