Pension and Other Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Employee benefits expense	$ 8	$ 10	$ 15	$ 20