Common Shares (Details) (USD $)	1 Months Ended	12 Months Ended
	Jul. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Common Shares
Shares purchased		10,375,000	0	0
Share price of shares purchased (in dollars per share)		$ 24.100
Total aggregate amount of shares purchased		$ 250,000,000
Preferred shares, shares issued		0
Issuance of common shares for stock options exercised (in shares)		3,000,000	600,000	1,100,000
Proceeds from stock options exercised		30,300,000	5,400,000	17,400,000
Amount paid to repurchase surrendered unexercised vested options to satisfy exercise price and related tax withholding obligations			21,000,000
Common stock dividend declared (in dollars per share)	$ 0.06	$ 0.04
Cash dividends paid		59,145,000	47,168,000
Officers and Directors
Common Shares
Restricted stock awarded to executive officers, key employees & directors		1,926,861	4,847,376	944,015
Restricted shares awarded, average market price (in dollars per share)		$ 19.53	$ 16.28	$ 20.69
Employees
Common Shares
Issuance of common shares for stock options exercised (in shares)			1,284	807,142
Value of surrendered unexercised vested stock options				$ 79,600,000