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)	170,791					173,094				(2,303)
Other comprehensive income	745							745
Total comprehensive income	171,536
Contributions by noncontrolling interests	29,342			6,647						22,695
Distributions to noncontrolling interests	(36,268)									(36,268)
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	101,832		2,124	102,937	(2,183)				(1,046)
Proceeds from issuance of common stock	1,394,465		29,493	1,364,972
Net proceeds from the issuance of preferred stock	696,437	718,750		(22,313)
Option compensation expense	1,641								1,641
Cash dividends paid:
Common stock cash dividends	(355,651)						(355,651)
Preferred stock cash dividends	(43,268)						(43,268)
Balances at end of period at Sep. 30, 2011	6,693,166	1,010,417	178,772	6,384,711	(13,535)	1,849,290	(2,826,800)	(10,354)	6,292	114,373
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)	188,805					190,077				(1,272)
Other comprehensive income	1,496							1,496
Total comprehensive income	190,301
Contributions by noncontrolling interests	26,751			80						26,671
Distributions to noncontrolling interests	(14,513)			(1,609)						(12,904)
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	98,980		1,784	102,238	(3,996)				(1,046)
Proceeds from issuance of common stock	3,447,408		64,400	3,383,008
Net proceeds from the issuance of preferred stock	277,687	287,500		(9,813)
Preferred stock redeemed, amount	(275,040)	(275,000)		6,202		(6,242)
Equity component of convertible debt	3,276		1,039	2,237
Option compensation expense	2,371								2,371
Cash dividends paid:
Common stock cash dividends	(460,936)						(460,936)
Preferred stock cash dividends	(52,527)						(52,527)
Balances at end of period at Sep. 30, 2012	$ 10,522,405	$ 1,022,917	$ 259,522	$ 10,502,057	$ (17,531)	$ 2,077,641	$ (3,485,592)	$ (10,432)	$ 7,445	$ 166,378