Changes in Equity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Changes in equity
Balance	$ 4,152,330	$ 3,861,429	$ 4,102,289	$ 3,930,586
Net income	139,598	130,111	172,434	129,630
Other comprehensive income (loss)	3,474	17,459	9,551	1,845
COMPREHENSIVE INCOME	143,072	147,570	181,985	131,475
Issuance of common stock	2,363	2,525	4,937	5,225
Reissuance of treasury stock - net	366	5,113	(5,905)	3,359
Other (primarily stock compensation)	185	631	15,010	3,981
Dividends on common Stock	(119,885)	(114,955)	(119,885)	(172,313)
Net capital activities by noncontrolling interests	(9,196)	(2,976)	(9,196)	(2,976)
Balance	4,169,235	3,899,337	4,169,235	3,899,337
Common Shareholders
Changes in equity
Balance	4,014,455	3,744,917	3,972,806	3,821,850
Net income	131,207	122,345	155,651	114,088
Other comprehensive income (loss)	3,474	17,459	9,551	1,845
COMPREHENSIVE INCOME	134,681	139,804	165,202	115,933
Issuance of common stock	2,363	2,525	4,937	5,225
Reissuance of treasury stock - net	366	5,113	(5,905)	3,359
Other (primarily stock compensation)	185	631	15,010	3,981
Dividends on common Stock	(119,885)	(114,955)	(119,885)	(172,313)
Balance	4,032,165	3,778,035	4,032,165	3,778,035
Noncontrolling Interests
Changes in equity
Balance	137,875	116,512	129,483	108,736
Net income	8,391	7,766	16,783	15,542
COMPREHENSIVE INCOME	8,391	7,766	16,783	15,542
Net capital activities by noncontrolling interests	(9,196)	(2,976)	(9,196)	(2,976)
Balance	$ 137,070	$ 121,302	$ 137,070	$ 121,302