Share Transactions (Details) (Common Shares, USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Common Shares
Class of Stock [Line Items]
Cumulative number of shares acquired since inception of share repurchase program	109,900,000
Aggregate purchase price of shares acquired since inception of share repurchase program	$ 2,790,000,000
Treasury stock, shares acquired (shares)		930,759
Treasury stock, value of shares acquired		41,000,000
Remaining authorized repurchase amount	$ 712,100,000