Real Estate (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011 properties acres sqft	Jun. 30, 2010 properties acres sqft	Jun. 30, 2011 properties sqft acres	Jun. 30, 2010 properties acres sqft	Dec. 31, 2010
Improved land	$ 5,035,181,000		$ 5,035,181,000		$ 2,527,972,000
Buildings and improvements	17,594,674,000		17,594,674,000		8,186,827,000
Properties under development, including cost of land	632,196,000		632,196,000		365,362,000
Land	2,033,725,000		2,033,725,000		1,533,611,000
Other real estate investments	452,978,000		452,978,000		265,869,000
Total investments in real estate properties	25,748,754,000		25,748,754,000		12,879,641,000
Less accumulated depreciation	1,764,289,000		1,764,289,000		1,595,678,000
Net investments in properties	23,984,465,000		23,984,465,000		11,283,963,000
Real Estate (Textuals) [Abstract]
Total number of industrial properties owned	1,898	985	1,898	985
Square feet of industrial properties	302,300,000	168,500,000	302,300,000	168,500,000
Square footage of industrial properties acquired in merger	81,100,000		81,100,000
Square footage of industrial properties acquired in PEPR acquisition	53,000,000		53,000,000
Total number of properties under development	23	14	23	14
Square feet of properties under development	8,600,000	4,900,000	8,600,000	4,900,000
Square footage of properties under development acquired in merger	3,700,000		3,700,000
Total expected investment upon completion of the properties under development			1,100,000,000
Total acres of land held	10,921	8,990	10,921	8,990
Acres of land held aquired in merger	2,257		2,257
Net gains on dispositions of investments in real estate	102,529,000	10,959,000	106,254,000	22,766,000
Japan disaster expense			5,600,000
Square feet of pre-stabilized completed porperties	1,500,000		1,500,000
Gain from the consolidation of PEPR			85,900,000
Gain from the acquisition of controlling interest in joint venture in Japan			$ 13,500,000