Real Estate - Real Estate Assets (Parenthetical) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013 Venture	Dec. 31, 2012
Real Estate Properties [Line Items]
Number of new ventures in foreign	2
Net investment in properties	$ 18,302,862,000	$ 23,328,463,000
Proceeds from contribution of properties for new ventures	4,900,000,000
Under Development Portfolio [Member]
Real Estate Properties [Line Items]
Square feet of properties	15,600,000	13,200,000
Number of properties under development	34	30
Pre-Stabilized Completed Properties [Member]
Real Estate Properties [Line Items]
Square feet of properties	2,600,000	4,800,000
Number of properties under development	8	15
Land held for future development [Member]
Real Estate Properties [Line Items]
Acreage of land held for development	10,605	10,915
Industrial Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	1,647	1,853
Square feet of properties	259,800,000	316,300,000
Japan and Europe [Member]
Real Estate Properties [Line Items]
Square feet of properties	58,300,000
Number of properties contributed for new ventures	207
Net investment in properties	$ 4,600,000,000