Stockholder's Equity (Summary of Dividend Payments) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of dividend payments
Dividends declared and paid per common share (in USD per share)	$ 3.4800	$ 3.4800	$ 3.4400
Common stock cash dividends	$ 1,300,141	$ 1,277,321	$ 1,233,519
Total dividend paid	$ 1,346,845	$ 1,326,731	$ 1,298,925
Series I Preferred Stock
Summary of dividend payments
Dividends declared and paid per Preferred share (in USD per share)	$ 3.2500	$ 3.2500	$ 3.2500
Preferred stock cash dividends	$ 46,704	$ 46,711	$ 46,719
Series J Preferred Stock
Summary of dividend payments
Dividends declared and paid per Preferred share (in USD per share)	$ 0	$ 0.2347	$ 1.6251
Preferred stock cash dividends	$ 0	$ 2,699	$ 18,687