Financings and Capitalization (Issuance of Common Stock) (Details) (Continuous Equity Program [Member], USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Continuous Equity Program [Member]
Aggregate sales price of an equity offering program		$ 50
Shares of common stock issued	650,235	762,925
Per share value of common stock issued	$ 23.07	$ 19.66
Value of common stock issued	$ 15	$ 15