Stockholder's Equity (Details 2) (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
Summary of dividend payments
Dividends declared and paid per common share	$ 0.715	$ 0.68	$ 1.405	$ 1.36
Common stock cash dividends			$ 228,565	$ 169,069
Total dividend paid			254,598	180,062
Series D Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share			$ 0.9844	$ 0.9844
Preferred stock cash dividends			3,937	3,938
Series E Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share				$ 0.7500
Preferred stock cash dividends				56
Series F Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share			$ 0.9532	$ 0.9532
Preferred stock cash dividends			6,672	6,672
Series G Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share				$ 0.9376
Preferred stock cash dividends				327
Series H Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share			$ 1.4293
Preferred stock cash dividends			500
Series I Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share			$ 1.0382
Preferred stock cash dividends			$ 14,924