Schedule III-Real Estate And Accumulated Depreciation (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Changes in real estate
Balance at beginning of year	$ 12,333,780,000	$ 11,662,953,000	$ 11,147,151,000
Property acquisitions	2,428,259,000	702,717,000	649,445,000
Improvements	379,295,000	199,141,000	146,410,000
Retirements/disposals/deconsolidation	(1,072,193,000)	(231,031,000)	(280,053,000)
Balance at end of year	14,069,141,000	12,333,780,000	11,662,953,000
Aggregate cost of land, buildings and improvements, before depreciation, for Federal income tax purposes	10,400,000,000
Changes in accumulated depreciation, exclusive of amounts relating to equipment, autos, and furniture and fixtures
Balance at beginning of year	1,646,240,000	1,393,323,000	1,136,603,000
Depreciation for year	307,823,000	286,776,000	288,560,000
Retirements/disposals/deconsolidation	(48,898,000)	(33,859,000)	(31,840,000)
Balance at end of year	$ 1,905,165,000	$ 1,646,240,000	$ 1,393,323,000