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, 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	(1,662)							(1,662)
Total comprehensive income	133,371
Net change in noncontrolling interests	17,089			80						17,009
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
Net proceeds from the issuance of preferred stock	277,688	287,500		(9,812)
Preferred stock redeemed, amount	(275,040)	(275,000)		6,202		(6,242)
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
Balances at beginning of period at Dec. 31, 2012	10,520,519	1,022,917	260,396	10,543,690	(17,875)	2,184,819	(3,694,579)	(11,028)	6,461	225,718
Comprehensive income:
Net income (loss)	79,746					79,754				(8)
Other comprehensive income	(42,600)							(38,146)		(4,454)
Total comprehensive income	37,146
Net change in noncontrolling interests	198,739									198,739
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	109,564		1,689	112,601	(3,373)				(1,353)
Proceeds from issuance of common stock	1,630,636		23,000	1,607,636
Net proceeds from the issuance of preferred stock	0
Option compensation expense	570								570
Cash dividends paid:
Common stock cash dividends	(399,815)						(399,815)
Preferred stock cash dividends	(33,203)						(33,203)
Balances at end of period at Jun. 30, 2013	$ 12,064,156	$ 1,022,917	$ 285,085	$ 12,263,927	$ (21,248)	$ 2,264,573	$ (4,127,597)	$ (49,174)	$ 5,678	$ 419,995