Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Capital in Excess of Par Value	Treasury Stock	Cumulative Net Income	Cumulative Dividends	Accumulated Other Comprehensive Income	Other Equity	Noncontrolling Interests
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)	139,563					145,050				(5,487)
Other comprehensive income	(20,000)							(13,503)		(6,497)
Total comprehensive Income	119,563
Net changes in noncontrolling interests	152,938		1,109	23,815						128,014
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	238,746		3,852	239,837	(3,388)				(1,555)
Net proceeds from sale of common stock	1,630,281		23,000	1,607,281
Equity component of convertible debt	(555)		988	(1,543)
Equity consideration in business combinations	0
Conversion of preferred stock	0	(5,556)	116	5,440
Option compensation expense	1,114								1,114
Cash dividends paid:
Common stock cash dividends	(839,939)						(839,939)
Preferred stock cash dividends	(66,336)						(66,336)
Balances at end of period at Dec. 31, 2013	11,756,331	1,017,361	289,461	12,418,520	(21,263)	2,329,869	(4,600,854)	(24,531)	6,020	341,748
Comprehensive income:
Net income (loss)	511,811					512,153				(342)
Other comprehensive income	(67,303)							(52,478)		(14,825)
Total comprehensive Income	444,508
Distributions to noncontrolling interests	(46,338)			(17,653)						(28,685)
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	287,530		4,958	297,975	(13,978)				(1,425)
Net proceeds from sale of common stock	2,063,982		33,925	2,030,057
Equity consideration in business combinations	1,193		258	935
Conversion of preferred stock	0	(11,111)	233	10,878
Option compensation expense	912								912
Cash dividends paid:
Common stock cash dividends	(969,661)						(969,661)
Preferred stock cash dividends	(65,408)						(65,408)
Balances at end of period at Dec. 31, 2014	13,473,049	1,006,250	328,835	14,740,712	(35,241)	2,842,022	(5,635,923)	(77,009)	5,507	297,896
Comprehensive income:
Net income (loss)	888,628					883,750				4,878
Other comprehensive income	(47,199)							(11,234)		(35,965)
Total comprehensive Income	841,429
Net changes in noncontrolling interests	295,439									318,516
Distributions to noncontrolling interests				(23,077)
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	298,184		4,400	305,022	(9,131)				(2,107)
Net proceeds from sale of common stock	1,470,458		20,246	1,450,212
Equity component of convertible debt	6,761		1,330	5,431
Option compensation expense	698								698
Cash dividends paid:
Common stock cash dividends	(1,144,727)						(1,144,727)
Preferred stock cash dividends	(65,406)						(65,406)
Balances at end of period at Dec. 31, 2015	$ 15,175,885	$ 1,006,250	$ 354,811	$ 16,478,300	$ (44,372)	$ 3,725,772	$ (6,846,056)	$ (88,243)	$ 4,098	$ 585,325