Consolidated Statements of Equity (Unaudited) (USD $) In Thousands, unless otherwise specified	Total	Preferred Stock	Common Stock	Capital in Excess of Par Value	Treasury Stock	Cumulative Net Income	Cumulative Dividends	Accumulated Other Comprehensive Income (Loss)	Other Equity	Noncontrolling Interests
Balances at beginning of period at Dec. 31, 2010	$ 4,733,100	$ 291,667	$ 147,155	$ 4,932,468	$ (11,352)	$ 1,676,196	$ (2,427,881)	$ (11,099)	$ 5,697	$ 130,249
Comprehensive income:
Net income (loss)	117,856					119,252				(1,396)
Other comprehensive income:
Unrealized gain (loss) on equity investments	86							86
Unrecognized gain (loss) on foreign currency translation	0
Cash flow hedge activity	868							868
Total comprehensive income	118,810
Contributions by noncontrolling interests	28,243			6,017						22,226
Distributions to noncontrolling interests	(16,227)									(16,227)
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	67,880		1,385	69,524	(2,141)				(888)
Proceeds from issuance of common stock	1,357,746		28,750	1,328,996
Proceeds from issuance of preferred stock	696,437	718,750		(22,313)
Preferred stock redeemed, amount	0	0
Conversion of preferred stock	0	0	0	0
Option compensation expense	1,651								1,651
Cash dividends paid:
Common stock cash dividends	(228,565)						(228,565)
Preferred stock cash dividends	(26,033)						(26,033)
Balances at end of period at Jun. 30, 2011	6,733,042	1,010,417	177,290	6,314,692	(13,493)	1,795,448	(2,682,479)	(10,145)	6,460	134,852
Balances at beginning of period at Dec. 31, 2011	7,278,647	1,010,417	192,299	7,019,714	(13,535)	1,893,806	(2,972,129)	(11,928)	6,120	153,883
Comprehensive income:
Net income (loss)	135,033					136,205				(1,172)
Other comprehensive income:
Unrealized gain (loss) on equity investments	(38)							(38)
Unrecognized gain (loss) on foreign currency translation	(2,348)							(2,348)
Cash flow hedge activity	724							724
Total comprehensive income	133,371
Contributions by noncontrolling interests	24,920			80						24,840
Distributions to noncontrolling interests	(7,831)									(7,831)
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	66,668		1,188	69,819	(3,737)				(602)
Proceeds from issuance of common stock	1,062,256		20,700	1,041,556
Proceeds from issuance of preferred stock	277,688	287,500		(9,812)
Preferred stock redeemed, amount	0	(275,000)		6,202		(6,242)
Conversion of preferred stock	(275,040)
Equity component of convertible debt	2,759		405	2,354
Option compensation expense	1,784								1,784
Cash dividends paid:
Common stock cash dividends	(301,503)						(301,503)
Preferred stock cash dividends	(35,926)						(35,926)
Balances at end of period at Jun. 30, 2012	$ 8,227,793	$ 1,022,917	$ 214,592	$ 8,129,913	$ (17,272)	$ 2,023,769	$ (3,309,558)	$ (13,590)	$ 7,302	$ 169,720