CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating revenues
Electric	$ 3,114,370	$ 3,055,045	$ 2,678,578
Natural gas	1,087,749	1,075,446	1,093,959
Steam and other	38,683	33,879	35,772
Total operating revenues	4,240,802	4,164,370	3,808,309
Operating expenses
Electric fuel and purchased power	1,425,173	1,513,334	1,399,541
Cost of natural gas sold and transported	692,096	685,210	712,079
Cost of sales - steam and other	17,552	16,995	15,426
Operating and maintenance expenses	734,729	677,359	628,999
Demand side management program expenses	115,078	128,939	104,919
Depreciation and amortization	328,582	284,139	256,062
Taxes (other than income taxes)	133,660	103,342	95,612
Total operating expenses	3,446,870	3,409,318	3,212,638
Operating income	793,932	755,052	595,671
Other income, net	7,001	29,117	4,696
Allowance for funds used during construction - equity	7,710	11,370	41,118
Interest charges and financing costs
Interest charges - includes other financing costs of $6,883, $5,649, and $5,686, respectively	186,885	171,945	166,212
Allowance for funds used during construction - debt	(3,406)	(5,307)	(18,452)
Total interest charges and financing costs	183,479	166,638	147,760
Income before income taxes	625,164	628,901	493,725
Income taxes	228,361	229,181	170,405
Net income	$ 396,803	$ 399,720	$ 323,320