Earnings Per Common Share Computation (Schedule of Details Supporting the Computation of Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Net income available for common stockholders	$ 460,287	$ 340,076	$ 775,463	$ 598,844
Weighted average outstanding shares of common stock used to compute basic earnings per common share	167,021	168,472	167,146	168,336
Shares used to compute diluted earnings per common share	169,560	170,229	169,547	170,154
Basic earnings per common share	$ 2.76	$ 2.02	$ 4.64	$ 3.56
Diluted earnings per common share	$ 2.71	$ 2.00	$ 4.57	$ 3.52
Number of antidilutive stock options and restricted stock excluded from computation	139	4,770	1,441	4,904
Employee Stock Options [Member]
Dilutive effect of employee stock options and restricted stock	1,073	533	996	566
Restricted Stock [Member]
Dilutive effect of employee stock options and restricted stock	1,466	1,224	1,405	1,252