Changes in Equity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Changes in equity
Balance at beginning of period	$ 3,861,429	$ 3,728,771	$ 3,930,586	$ 3,775,226
Net income	130,111	93,839	129,630	84,165
Other comprehensive income	17,459	6,646	1,845	17,092
COMPREHENSIVE INCOME	147,570	100,485	131,475	101,257
Issuance of capital stock	2,525	3,505	5,225	17,065
Reissuance of treasury stock - net	5,113		3,359	(3,530)
Other (primarily stock compensation)	631	(33)	3,981	(181)
Dividends on common stock	(114,955)	(114,509)	(172,313)	(171,618)
Net capital activities by noncontrolling interests	(2,976)	(2,609)	(2,976)	(2,609)
Balance at end of period	3,899,337	3,715,610	3,899,337	3,715,610
Common Shareholders
Changes in equity
Balance at beginning of period	3,744,917	3,631,411	3,821,850	3,683,327
Net income	122,345	86,685	114,088	71,550
Other comprehensive income	17,459	6,646	1,845	17,092
COMPREHENSIVE INCOME	139,804	93,331	115,933	88,642
Issuance of capital stock	2,525	3,505	5,225	17,065
Reissuance of treasury stock - net	5,113		3,359	(3,530)
Other (primarily stock compensation)	631	(33)	3,981	(181)
Dividends on common stock	(114,955)	(114,509)	(172,313)	(171,618)
Balance at end of period	3,778,035	3,613,705	3,778,035	3,613,705
Noncontrolling Interests
Changes in equity
Balance at beginning of period	116,512	97,360	108,736	91,899
Net income	7,766	7,154	15,542	12,615
COMPREHENSIVE INCOME	7,766	7,154	15,542	12,615
Net capital activities by noncontrolling interests	(2,976)	(2,609)	(2,976)	(2,609)
Balance at end of period	$ 121,302	$ 101,905	$ 121,302	$ 101,905