Basis of Presentation and Significant Accounting Policies (Details 2) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Tax Treatment Of Dividend [Line Items]
Minimum Percentage of Taxable Income Distributed As Dividends	90.00%								90.00%
Income Tax Expense Benefit Continuing Operations Income Tax Reconciliation [Line Items]
Net (Loss) Income Attributable to Common Shareholders	$ (68,887,000)	$ 83,005,000	$ 145,926,000	$ 231,990,000	$ 62,633,000	$ 232,393,000	$ 20,510,000	$ 233,735,000	$ 392,034,000	$ 549,271,000	$ 601,771,000
Depreciation and Amortization									155,401,000	205,155,000	225,802,000
Impairment losses on marketable equity securities									37,236,000	211,328,000	0
Straight-line rent adjustments									(64,811,000)	(64,679,000)	(38,800,000)
Earnings of Partially Owned Entities									339,376,000	(60,049,000)	(96,178,000)
Stock Options									4,884,000	(28,701,000)	(27,697,000)
Sale of Real Estate									(324,936,000)	(123,905,000)	(18,766,000)
Derivatives									31,578,000	71,228,000	(12,160,000)
Mortgage and mezzanine loans receivable									0	0	(82,512,000)
Other, net									4,608,000	17,080,000	(6,223,000)
Estimated Taxable Income (unaudited)									575,370,000	776,728,000	545,237,000
Income Tax Liability Relating to Taxable REIT Subsidiaries Current									9,608,000	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 $3.6 billion lower than the amounts reported in our consolidated
Net Basis Difference Of Assets And Liabilities Between Tax Basis And GAAP Basis	$ 3,600,000,000								$ 3,600,000,000
Ordinary Income [Member]
Tax Treatment Of Dividend [Line Items]
Percentage Of Taxable Income Distributed									100.00%	62.70%	93.20%
Long Term Capital Gain [Member]
Tax Treatment Of Dividend [Line Items]
Percentage Of Taxable Income Distributed										37.30%	6.80%