Derivative Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Cash Flow Hedging	Mar. 31, 2012 Cash Flow Hedging	Sep. 30, 2012 Balance Sheet Hedging	Mar. 31, 2012 Balance Sheet Hedging	Sep. 30, 2012 Nondesignated British Pounds Sterling Balance Sheet Hedging	Mar. 31, 2012 Nondesignated British Pounds Sterling Balance Sheet Hedging	Sep. 30, 2012 Nondesignated United States Dollar Balance Sheet Hedging	Mar. 31, 2012 Nondesignated United States Dollar Balance Sheet Hedging
Derivative
Maturity period, maximum (in months)	15 months
Notional value of foreign currency purchase contracts		$ 53	$ 74						$ 37
Notional value of foreign currency sale contracts		94	78			9	8	343	197
Foreign currency option contracts outstanding			2
Notional value of foreign currency forward contracts				$ 352	$ 242