Real Estate and Accumulated Depreciation (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investment in real estate:
Balance at beginning of year	$ 23,734,733,000	$ 18,082,399,000	$ 14,844,319,000
Additions:
Acquisitions	2,210,600,000	3,597,955,000	2,923,251,000
Improvements	380,298,000	408,844,000	449,964,000
Assumed other items, net	160,897,000	772,972,000	108,404,000
Assumed debt	265,152,000	1,340,939,000	481,598,000
Total additions	3,016,947,000	6,154,628,000	2,506,861,000
Deductions:
Cost of real estate sold	(916,997,000)	(498,564,000)	(581,696,000)
Reclassification of accumulated depreciation and amortization for assets held for sale	(64,476,000)	(3,730,000)	(120,236,000)
Impairment of assets	0	0	(29,287,000)
Total deductions	(981,473,000)	(502,294,000)	(731,219,000)
Foreign currency translation on real estate, net	(278,272,000)	33,918,000	6,082,000
Balance at end of year	25,491,935,000	23,734,733,000	18,082,399,000
Accumulated depreciation:
Balance at beginning of year	2,386,658,000	1,555,055,000	1,194,476,000
Additions:
Depreciation and amortization expenses	844,130,000	873,960,000	533,585,000
Amortization of above market leases	7,935,000	7,831,000	7,204,000
Total additions	852,065,000	881,791,000	540,789,000
Deductions:
Sale of properties	(123,582,000)	(49,625,000)	(59,974,000)
Reclassification of accumulated depreciation and amortization for assets held for sale	(64,476,000)	(3,730,000)	(120,236,000)
Total deductions	(188,058,000)	(53,355,000)	(180,210,000)
Foreign currency translation on accumulated depreciation, net	(29,757,000)	3,167,000	0
Balance at end of year	3,020,908,000	2,386,658,000	1,555,055,000
Accumulated depreciation	3,020,908,000	2,386,658,000
Reconciliation of real property (Textual) [Abstract]
Aggregate cost for tax purposes for real property	$ 20,260,297,000	$ 14,788,080,000	$ 13,604,448,000