Equity - Preferred Stock Table (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred Stock, Shares Outstanding, Beginning of Period	5,839,506
Preferred Stock, Shares Outstanding, End of Period	5,603,458	5,839,506
Loss on Exchange of Preferred Stock	$ (41,000,000)	$ (428,000,000)	$ 0
5.75% Cumulative Convertible Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred Stock, Dividend Rate, Percentage	5.75%
5.75% Cumulative Convertible Preferred Stock Series A [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred Stock, Dividend Rate, Percentage	5.75%
4.50% Cumulative Convertible Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred Stock, Dividend Rate, Percentage	4.50%
5.0% Cumulative Convertible Preferred Stock Series 2005 B [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred Stock, Dividend Rate, Percentage	5.00%
Preferred Stock [Member] | 5.75% Cumulative Convertible Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred Stock, Shares Outstanding, Beginning of Period	843,000	1,497,000	1,497,000
Conversion of Stock, Shares Converted	(72,600)	653,872
Preferred Stock, Shares Outstanding, End of Period	770,000	843,000	1,497,000
Preferred Stock, Dividend Rate, Percentage	5.75%
Loss on Exchange of Preferred Stock	$ (32.7573)
Preferred Stock [Member] | 5.75% Cumulative Convertible Preferred Stock Series A [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred Stock, Shares Outstanding, Beginning of Period	476,000	1,100,000	1,100,000
Conversion of Stock, Shares Converted	(12,500)	624,137
Preferred Stock, Shares Outstanding, End of Period	463,000	476,000	1,100,000
Preferred Stock, Dividend Rate, Percentage	5.75%
Loss on Exchange of Preferred Stock	$ (33.8976)
Preferred Stock [Member] | 4.50% Cumulative Convertible Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred Stock, Shares Outstanding, Beginning of Period	2,559,000	2,559,000	2,559,000
Conversion of Stock, Shares Converted	0	0
Preferred Stock, Shares Outstanding, End of Period	2,559,000	2,559,000	2,559,000
Loss on Exchange of Preferred Stock	$ (52.9298)
Preferred Stock [Member] | 5.0% Cumulative Convertible Preferred Stock Series 2005 B [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred Stock, Shares Outstanding, Beginning of Period	1,962,000	2,096,000	2,096,000
Conversion of Stock, Shares Converted	(150,948)	134,000
Preferred Stock, Shares Outstanding, End of Period	1,811,000	1,962,000	2,096,000
Loss on Exchange of Preferred Stock	$ (46.8560)
Common Stock [Member] | 5.75% Cumulative Convertible Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, Conversion of Convertible Securities	7,442,156	59,141,429
Common Stock [Member] | 5.75% Cumulative Convertible Preferred Stock Series A [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, Conversion of Convertible Securities	1,205,923	60,032,734
Common Stock [Member] | 5.0% Cumulative Convertible Preferred Stock Series 2005 B [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, Conversion of Convertible Securities	1,317,756	1,012,032