Basis of Presentation and Significant Accounting Policies (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property Plant And Equipment [Line Items]
Impairment losses, acquisition related costs and tenant buy-outs									$ 120,786,000	$ 35,299,000	$ 109,458,000
Net gain on disposition of wholly owned and partially owned assets									13,347,000	15,134,000	81,432,000
Identified Intangibles
Identified Intangible Assets, Net	370,602,000				287,844,000				370,602,000	287,844,000
Identified Intangible Liabilities (included in deferred credit)	463,432,000				466,743,000				463,432,000	466,743,000
Significant Policies Other Details [Abstract]
Accounts receivable, allowance for doubtful accounts	37,674,000				43,241,000				37,674,000	43,241,000
Receivables Arising From Straight Lining Of Rents Allowance	3,165,000				3,290,000				3,165,000	3,290,000
Condominium Assets held for sale	53,737,000				60,785,000				53,737,000	60,785,000
Tax Treatment Of Dividend [Line Items]
Percent of dividend paid to Shareholders	100.00%				100.00%				100.00%	100.00%	100.00%
Minimum Percentage of Taxable Income Distributed As Dividends	90.00%								90.00%
Income Tax Expense Benefit Continuing Operations Income Tax Reconciliation [Line Items]
NET INCOME attributable to common shareholders	62,633,000	232,393,000	20,510,000	233,735,000	69,508,000	41,135,000	91,913,000	399,215,000	549,271,000	601,771,000	596,731,000
Depreciation and Amortization									205,155,000	225,802,000	216,473,000
Income Tax Reconciliation, Nondeductible Expense, Impairment Losses									211,328,000	0	0
Mezzanine Loans Receivable									0	(82,512,000)	(104,727,000)
Straight-line Rent Adjustment									(64,679,000)	(38,800,000)	(70,606,000)
Earnings of Partially Owned Entities									(60,049,000)	(96,178,000)	(62,315,000)
Stock Options									(28,701,000)	(27,697,000)	(48,399,000)
Sale of Real Estate									(123,905,000)	(18,766,000)	12,899,000
Derivatives									71,228,000	(12,160,000)	(121,120,000)
Other Adjustments									17,080,000	(6,223,000)	48,915,000
Estimated Taxable Income Net									776,728,000	545,237,000	467,851,000
Income Tax Liability Relating to Taxable REIT Subsidiaries Current	20,336,000				26,645,000				20,336,000	26,645,000
Explanation Differences Between Book And Tax Basis									The net basis of our assets and liabilities for tax reporting purposes is approximately $3.8 billion lower than its amount reported in our consolidated financial statements
Net Basis Difference Of Assets And Liabilities Between Tax Basis And GAAP Basis	3,000,000,000								3,000,000,000
Ordinary Income [Member]
Tax Treatment Of Dividend [Line Items]
Percent of dividend paid to Shareholders	62.70%				93.20%				62.70%	93.20%	95.90%
Long Term Capital Gain [Member]
Tax Treatment Of Dividend [Line Items]
Percent of dividend paid to Shareholders	37.30%				6.80%				37.30%	6.80%	2.80%
Return Of Capital [Member]
Tax Treatment Of Dividend [Line Items]
Percent of dividend paid to Shareholders	0.00%				0.00%				0.00%	0.00%	1.30%
Equity Method Investments [Member]
Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net By Investment Category [Line Items]
Other than Temporary Impairment Losses, Investments									4,936,000	13,794,000	11,481,000
Real Estate [Member]
Property Plant And Equipment [Line Items]
Impairment losses, acquisition related costs and tenant buy-outs									107,000,000	0	72,500,000
Cost Of Real Estate Acquisitions Not Consummated [Member]
Property Plant And Equipment [Line Items]
Impairment losses, acquisition related costs and tenant buy-outs									11,248,000	32,259,000	6,945,000
Development Related Real Estate [Member]
Property Plant And Equipment [Line Items]
Impairment losses, acquisition related costs and tenant buy-outs									0	3,040,000	0
Condominium Units [Member]
Property Plant And Equipment [Line Items]
Impairment losses, acquisition related costs and tenant buy-outs									2,538,000	0	30,013,000
Net gain on disposition of wholly owned and partially owned assets									$ 1,274,000	$ 5,884,000	$ 3,149,000