Capital Transactions (Details) (USD $)	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2012 Share Repurchase Program	Mar. 31, 2012 Share Repurchase Program	Mar. 31, 2013 New Share Repurchase Program	Mar. 31, 2013 New Share Repurchase Program
Share Repurchase Program [Line Items]
Stock repurchase program, dollar amount authorized		$ 1,500,000,000		$ 1,000,000,000
Cost of common stock repurchased under the stock repurchase program	$ 261,000,000		$ 0
Shares of common stock repurchased	22,000,000		0