Equity (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Increase (decrease) in equity
Balance, at beginning of period			$ 5,544,288
Public offering of common stock			1,213,851
Other			26,859
Purchase of noncontrolling interest	(4,667)		(4,667)
Distributions to common shareholders and limited partners, excluding Operating Partnership preferred interests			(703,098)
Distributions to other noncontrolling interest partners			(191)
Comprehensive income, excluding $958 attributable to preferred interests in the Operating Partnership and $3965 attributable to noncontrolling redeemable interests in properties in temporary equity			1,053,557
Balance, at end of period	7,130,599		7,130,599
Comprehensive income attributable to noncontrolling interests	33,025	49,743	183,350	92,016
Preferred Stock
Increase (decrease) in equity
Balance, at beginning of period			45,047
Other			(164)
Balance, at end of period	44,883		44,883
Comprehensive income attributable to preferred interests			958
Common Stock
Increase (decrease) in equity
Balance, at beginning of period			30
Public offering of common stock			1
Balance, at end of period	31		31
Accumulated Other Comprehensive Income
Increase (decrease) in equity
Balance, at beginning of period			(94,263)
Comprehensive income, excluding $958 attributable to preferred interests in the Operating Partnership and $3965 attributable to noncontrolling redeemable interests in properties in temporary equity			12,607
Balance, at end of period	(81,656)		(81,656)
Capital in Excess of Par Value
Increase (decrease) in equity
Balance, at beginning of period			8,103,133
Exchange of limited partner units for common shares			4,018
Public offering of common stock			1,213,850
Other			(9,541)
Purchase of noncontrolling interest	(63,226)		(63,226)
Adjustment to limited partners' interest from increased ownership in the Operating Partnership			(156,299)
Balance, at end of period	9,091,935		9,091,935
Accumulated Deficit
Increase (decrease) in equity
Balance, at beginning of period			(3,251,740)
Other			(931)
Distributions to common shareholders and limited partners, excluding Operating Partnership preferred interests			(584,084)
Comprehensive income, excluding $958 attributable to preferred interests in the Operating Partnership and $3965 attributable to noncontrolling redeemable interests in properties in temporary equity			862,524
Balance, at end of period	(2,974,231)		(2,974,231)
Common Stock Held in Treasury
Increase (decrease) in equity
Balance, at beginning of period			(152,541)
Other			16,760
Balance, at end of period	(135,781)		(135,781)
Noncontrolling interests
Increase (decrease) in equity
Balance, at beginning of period	1,215,628	771,152	894,622	802,972
Exchange of limited partner units for common shares	(2,600)	(3,712)	(4,018)	(5,923)
Other			20,735
Purchase of noncontrolling interest	58,559		58,559
Adjustment to limited partners' interest from increased ownership in the Operating Partnership			156,299
Distributions to common shareholders and limited partners, excluding Operating Partnership preferred interests			(119,014)
Distributions to other noncontrolling interest partners			(191)
Comprehensive income, excluding $958 attributable to preferred interests in the Operating Partnership and $3965 attributable to noncontrolling redeemable interests in properties in temporary equity			178,426
Balance, at end of period	1,185,418	773,894	1,185,418	773,894
Comprehensive income attributable to noncontrolling interests			$ 3,965