CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
NET INCOME	$ 413,164	$ 366,940	$ 370,209
Derivative instruments:
Net unrealized loss, net of tax benefit of $14,900, $37,389 and $61,348 (Note 18)	(22,763)	(57,271)	(93,939)
Reclassification of net realized loss, net of tax benefit of $39,120, $46,288 and $48,453 (Note 18)	59,887	70,902	74,287
Pension and other postretirement benefits activity, net of tax (expense) benefit of $(651), $3,935 and $5,608 (Note 8)	1,031	(6,026)	(8,528)
Total other comprehensive income (loss)	38,155	7,605	(28,180)
COMPREHENSIVE INCOME	451,319	374,545	342,029
Less: Comprehensive income attributable to noncontrolling interests	31,622	27,467	20,156
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 419,697	$ 347,078	$ 321,873