Shareholders' Equity Preferred Stock (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock	$ 0	$ 446,592,000	$ 177,955,000
Other Preferred Stock Dividends and Adjustments	$ 0	13,752,000	5,932,000
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%
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)