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, 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
Decrease in 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	7,644		337	22,710	(13,978)				(1,425)
Net proceeds from sale of common stock	2,343,868		38,546	2,305,322
Equity component of convertible debt	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
Increase in noncontrolling interests	295,439									318,516
Decrease in noncontrolling interests				(23,077)
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	13,941		126	25,053	(9,131)				(2,107)
Net proceeds from sale of common stock	1,754,701		24,520	1,730,181
Equity component of convertible debt	6,761			5,431
Equity componenet of convertible debt - common stock			1,330
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
Comprehensive income:
Net income (loss)	1,087,080					1,077,803				9,277
Other comprehensive income	(78,833)							(81,288)		2,455
Total comprehensive Income	1,008,247
Decrease in noncontrolling interests	(173,456)			(51,478)						(121,978)
Amounts related to issuance of common stock from dividend reinvestment and stock incentive plans, net of forfeitures	36,103		839	46,938	(10,369)				(1,305)
Net proceeds from sale of common stock	533,352		7,421	525,931
Option compensation expense	266								266
Cash dividends paid:
Common stock cash dividends	(1,233,519)						(1,233,519)
Preferred stock cash dividends	(65,406)						(65,406)
Balances at end of period at Dec. 31, 2016	$ 15,281,472	$ 1,006,250	$ 363,071	$ 16,999,691	$ (54,741)	$ 4,803,575	$ (8,144,981)	$ (169,531)	$ 3,059	$ 475,079