Changes in Equity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Changes in equity
Balance at beginning of period	$ 3,899,337	$ 3,715,610	$ 3,930,586	$ 3,775,226
Net income	252,863	262,785	382,493	346,950
Other comprehensive income	30,843	21,131	32,688	38,224
COMPREHENSIVE INCOME	283,706	283,916	415,181	385,174
Issuance of capital stock	2,365	3,789	7,590	20,854
Reissuance (purchase) of treasury stock - net	(82)	537	3,277	(2,993)
Other (primarily stock compensation)	258	(436)	4,270	(606)
Dividends on common stock			(172,344)	(171,630)
Net capital activities by noncontrolling interests		(421)	(2,976)	(3,030)
Balance at end of period	4,185,584	4,002,995	4,185,584	4,002,995
Common Shareholders
Changes in equity
Balance at beginning of period	3,778,035	3,613,705	3,821,850	3,683,327
Net income	244,823	255,359	358,911	326,909
Other comprehensive income	30,843	21,131	32,688	38,224
COMPREHENSIVE INCOME	275,666	276,490	391,599	365,133
Issuance of capital stock	2,365	3,789	7,590	20,854
Reissuance (purchase) of treasury stock - net	(82)	537	3,277	(2,993)
Other (primarily stock compensation)	258	(436)	4,270	(606)
Dividends on common stock			(172,344)	(171,630)
Balance at end of period	4,056,242	3,894,085	4,056,242	3,894,085
Noncontrolling Interests
Changes in equity
Balance at beginning of period	121,302	101,905	108,736	91,899
Net income	8,040	7,426	23,582	20,041
COMPREHENSIVE INCOME	8,040	7,426	23,582	20,041
Net capital activities by noncontrolling interests		(421)	(2,976)	(3,030)
Balance at end of period	$ 129,342	$ 108,910	$ 129,342	$ 108,910