CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
NET INCOME	$ 252,863	$ 262,785	$ 382,493	$ 346,950
Derivative instruments:
Net unrealized loss, net of tax benefit of $47 and $10,055 for three months ended September 30, 2012 and 2011 and $14,817 and $16,113 for nine months ended September 30, 2012 and 2011, respectively	(72)	(15,402)	(22,696)	(24,679)
Reclassification of net realized loss, net of tax benefit of $19,543 and $23,361 for three months ended September 30, 2012 and 2011 and $34,361 and $39,213 for nine months ended September 30, 2012 and 2011, respectively	29,935	35,783	52,632	60,065
Pension and other postretirement benefits activity, net of tax expense of $640 and $489 for three months ended September 30, 2012 and 2011 and $1,797 and $1,853 for nine months ended September 30, 2012 and 2011, respectively	980	750	2,752	2,838
Total other comprehensive income	30,843	21,131	32,688	38,224
COMPREHENSIVE INCOME	283,706	283,916	415,181	385,174
Less: Comprehensive income attributable to noncontrolling interests	8,040	7,426	23,582	20,041
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 275,666	$ 276,490	$ 391,599	$ 365,133