Stockholder's Equity (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of dividend payments
Dividends declared and paid per common share	$ 3.18	$ 3.06	$ 2.96
Common stock cash dividends	$ 969,661,000	$ 839,939,000	$ 653,321,000
Total dividend paid	1,035,069,000	906,275,000	722,450,000
Series D Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share	$ 0	$ 0	$ 0.50301
Preferred stock cash dividends	0	0	2,012,000
Series F Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share	$ 0	$ 0	$ 0.48715
Preferred stock cash dividends	0	0	3,410,000
Series H Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share	$ 0.00794	$ 2.8584	$ 2.8584
Preferred stock cash dividends	1,000	930,000	1,000,000
Series I Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share	$ 3.25	$ 3.25	$ 3.25
Preferred stock cash dividends	46,719,000	46,719,000	46,719,000
Series J Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share	$ 1.6251	$ 1.6251	$ 1.39038
Preferred stock cash dividends	$ 18,688,000	$ 18,687,000	$ 15,988,000