Stockholder's Equity (Details 3) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of dividend payments
Dividends declared and paid per common share	$ 3.48	$ 3.44	$ 3.3
Common stock cash dividends	$ 1,277,321	$ 1,233,519	$ 1,144,727
Total dividend paid	$ 1,326,731	$ 1,298,925	$ 1,210,133
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	$ 46,711	$ 46,719	$ 46,719
Series J Preferred Stock [Member]
Summary of dividend payments
Dividends declared and paid per Preferred share	$ 0.2347	$ 1.6251	$ 1.6251
Preferred stock cash dividends	$ 2,699	$ 18,687	$ 18,687