Real Estate and Accumulated Depreciation (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investment in real estate:
Balance at beginning of year	$ 18,082,399,000	$ 14,844,319,000	$ 8,992,495,000
Additions:
Acquisitions	3,597,955,000	2,923,251,000	4,525,737,000
Improvements	408,844,000	449,964,000	426,000,000
Assumed other items, net	772,972,000	108,404,000	210,411,000
Assumed debt	1,340,939,000	481,598,000	961,928,000
Total additions	6,154,628,000	3,969,299,000	6,124,076,000
Deductions:
Cost of real estate sold	(498,564,000)	(581,696,000)	(250,047,000)
Reclassification of accumulated depreciation and amortization for assets held for sale	(3,730,000)	(120,236,000)	(10,011,000)
Impairment of assets	0	(29,287,000)	(12,194,000)
Total deductions	(502,294,000)	(731,219,000)	(272,252,000)
Foreign currency translation on real estate, net	33,918,000	6,082,000	0
Balance at end of year	23,734,733,000	18,082,399,000	14,844,319,000
Additions:
Depreciation and amortization expenses	873,960,000	533,585,000	423,605,000
Amortization of above market leases	7,831,000	7,204,000	6,409,000
Total additions	881,791,000	540,789,000	430,014,000
Deductions:
Sale of properties	(49,625,000)	(59,974,000)	(63,997,000)
Reclassification of accumulated depreciation and amortization for assets held for sale	(3,730,000)	(120,236,000)	(8,507,000)
Total deductions	(53,355,000)	(180,210,000)	(72,504,000)
Foreign currency translation on accumulated depreciation, net	3,167,000	0	0
Accumulated depreciation	2,386,658,000	1,555,055,000	1,194,476,000	836,966,000
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