Shareholders' Equity Preferred Stock (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock	$ 446,592,000	$ 177,955,000	$ 168,272,000
Other Preferred Stock Dividends and Adjustments	13,752,000	5,932,000	5,730,000
Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock	17,700,000
Preferred Stock, Redemption Price Per Share	$ 250
Stock Repurchased During Period, Shares	750,243
Stock Repurchased During Period, Value	18,800,000
Series J Preferred Stock [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock	96,100,000
Other Preferred Stock Dividends and Adjustments	3,200,000
Stock Redeemed or Called During Period, Shares	384,530
Preferred Stock, Dividend Rate, Percentage	6.625%
Series K Preferred Stock [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock	149,400,000
Other Preferred Stock Dividends and Adjustments	5,000,000
Stock Redeemed or Called During Period, Shares	597,579
Preferred Stock, Dividend Rate, Percentage	6.50%
Series L Preferred Stock [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock	183,400,000
Other Preferred Stock Dividends and Adjustments	6,000,000
Stock Redeemed or Called During Period, Shares	733,597
Preferred Stock, Dividend Rate, Percentage	6.60%
Series O Preferred Stock [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock		178,000,000
Other Preferred Stock Dividends and Adjustments		5,900,000
Preferred Stock, Dividend Rate, Percentage		8.375%
Series M Preferred Stock [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock			168,300,000
Other Preferred Stock Dividends and Adjustments			5,700,000
Preferred Stock, Dividend Rate, Percentage			6.95%
Issuance Costs [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Other Preferred Stock Dividends and Adjustments	618,000
Gain (Loss) Repurchase of Redeemable Preferred Shares (Member) | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Other Preferred Stock Dividends and Adjustments	$ (483,000)