Dispositions - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended		1 Months Ended
	Dec. 31, 2010 sqft Property	Dec. 31, 2012 sqft Property	Dec. 31, 2011 Property sqft	Dec. 31, 2010 Shopping centers [Member] Property	Dec. 31, 2010 Office buildings [Member] Property	Dec. 31, 2010 Mixed-use projects [Member] Property	Dec. 31, 2010 Residential development joint ventures [Member] Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed	182	200	94
Real estate property disposed (in square feet)	23,000,000	27,200,000	10,700,000
Gross proceeds from selling of a portfolio	$ 1,000,000,000	$ 1,700,000,000	$ 1,100,000,000
Net gain achieved	203,100,000	83,200,000	74,000,000
Gain (Loss) from continuing operations	(66,100,000)	17,300,000	9,500,000
Gain from discontinued operations	269,200,000	65,900,000	64,500,000
Number of properties to be sold				4	2	11	2
Impairment charge	168,800,000
Gain (Loss) on disposition of property			$ 4,400,000
Percentage of ownership interest	20.00%
Number of properties under equity method investments	3