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	$ 7,281,647	$ 1,010,417	$ 192,299	$ 7,019,714	$ (13,535)	$ 1,896,806	$ (2,972,129)	$ (11,928)	$ 6,120	$ 153,883
Comprehensive income:
Net income (loss)	57,836					58,514				(678)
Other comprehensive income	286							286
Total comprehensive income	58,122
Net change in noncontrolling interests	5,302			874						4,428
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	32,052		530	35,546	(3,730)				(294)
Proceeds from issuance of common stock	1,062,738		20,700	1,042,038
Net proceeds from the issuance of preferred stock	277,901	287,500		(9,599)
Option compensation expense	1,382								1,382
Cash dividends paid:
Common stock cash dividends	(142,919)						(142,919)
Preferred stock cash dividends	(19,207)						(19,207)
Balances at end of period at Mar. 31, 2012	8,557,018	1,297,917	213,529	8,088,573	(17,265)	1,955,320	(3,134,255)	(11,642)	7,208	157,633
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)	72,220					71,660				560
Other comprehensive income	(22,063)							(22,063)
Total comprehensive income	50,157
Net change in noncontrolling interests	(23,903)									(23,903)
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	52,228		853	55,600	(3,363)				(862)
Net proceeds from the issuance of preferred stock	0
Option compensation expense	294								294
Cash dividends paid:
Common stock cash dividends	(199,546)						(199,546)
Preferred stock cash dividends	(16,602)						(16,602)
Balances at end of period at Mar. 31, 2013	$ 10,383,147	$ 1,022,917	$ 261,249	$ 10,599,290	$ (21,238)	$ 2,256,479	$ (3,910,727)	$ (33,091)	$ 5,893	$ 202,375