Share Transactions (Details) (USD $)	9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2011 Common Shares	Sep. 30, 2010 Common Shares	Sep. 30, 2011 Common Shares	Sep. 30, 2010 Common Shares
Three-for-one share split:
Share split, ratio	three-for-one
Authorized common shares	600,000,000
Authorized common shares pre split	200,000,000
Common shares par	$ 0.0033	$ 0.0033
Common shares par, pre split	$ 0.01
Share repurchases:
Treasury stock, shares, acquired			700,000	2,000,000	9,600,000	20,600,000
Treasury stock, value, acquired, cost method			$ 20,800,000	$ 53,400,000	$ 287,600,000	$ 503,700,000
Treasury stock, shares, cumulative amount acquired					104,800,000
Treasury stock, aggregate purchase price, cumulative	2,560,000,000
Stock repurchase program, remaining authorized repurchase amount					$ 942,000,000