Real Estate and Accumulated Depreciation - (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Real Estate
Balance at beginning of year	$ 8,214,081,000		$ 8,333,419,000		$ 8,917,137,000
Additions during the year:
Acquisitions	379,187,000		66,058,000		131,374,000
Capital additions	367,454,000		376,038,000		272,103,000
Deductions during the year:
Casualty and other write-offs	(111,068,000)	[1]	(98,489,000)	[1]	(62,589,000)	[1]
Reclassification of real estate included in sale of asset management business	0		0		(160,420,000)
SEC Schedule III, Real Estate, Held For Sale	(38,744,000)		0		0
Sales	(665,952,000)		(462,945,000)		(764,186,000)
Balance at end of year	8,144,958,000		8,214,081,000		8,333,419,000
Accumulated Depreciation
Balance at beginning of year	2,822,872,000		2,820,765,000		2,872,190,000
Additions during the year
Depreciation	265,060,000		288,666,000		353,414,000
Deductions during the year:
Casualty and other write-offs	(106,802,000)	[1]	(92,775,000)	[1]	(46,869,000)	[1]
Reclassification of real estate included in sale of asset management business	0		0		(33,394,000)
SEC Schedule III, Accumulated Depreciation, Held For Sale	(12,304,000)		0		0
Sales	(296,647,000)		(193,784,000)		(324,576,000)
Balance at end of year	2,672,179,000		2,822,872,000		2,820,765,000
Write-off of fully depreciated assets	$ 106,300,000		$ 91,900,000		$ 38,700,000

[1] Includes the write-off of fully depreciated assets totaling $106.3 million, $91.9 million and $38.7 million, during the years ended December 31, 2014, 201