CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating revenues
Electric	$ 8,517,296	$ 8,766,593	$ 8,451,845
Natural gas	1,537,374	1,811,926	1,782,582
Other	73,553	76,251	76,520
Total operating revenues	10,128,223	10,654,770	10,310,947
Operating expenses
Electric fuel and purchased power	3,623,935	3,991,786	4,010,660
Cost of natural gas sold and transported	880,939	1,163,890	1,162,926
Cost of sales - other	29,067	30,391	29,540
Operating and maintenance expenses	2,176,095	2,140,289	2,057,249
Conservation and demand side management program expenses	260,527	281,378	239,827
Depreciation and amortization	926,053	890,619	858,882
Taxes (other than income taxes)	408,924	374,815	331,894
Total operating expenses	8,305,540	8,873,168	8,690,978
Operating income	1,822,683	1,781,602	1,619,969
Other income, net	6,175	9,255	31,143
Equity earnings of unconsolidated subsidiaries	29,971	30,527	29,948
Allowance for funds used during construction - equity	62,840	51,223	56,152
Interest charges and financing costs
Interest charges - includes other financing costs of $24,087, $24,019, and $20,638, respectively	601,582	591,098	577,291
Allowance for funds used during construction - debt	(35,315)	(28,181)	(28,670)
Total interest charges and financing costs	566,267	562,917	548,621
Income from continuing operations before income taxes	1,355,402	1,309,690	1,188,591
Income taxes	450,203	468,316	436,635
Income from continuing operations	905,199	841,374	751,956
Income (loss) from discontinued operations, net of tax	30	(202)	3,878
Net income	905,229	841,172	755,834
Dividend requirements on preferred stock	0	3,534	4,241
Premium on redemption of preferred stock	0	3,260	0
Earnings available to common shareholders	$ 905,229	$ 834,378	$ 751,593
Weighted average common shares outstanding:
Basic (in shares)	487,899	485,039	462,052
Diluted (in shares)	488,434	485,615	463,391
Earnings per average common share - basic:
Income from continuing operations (in dollars per share)	$ 1.86	$ 1.72	$ 1.62
Income from discontinued operations (in dollars per share)	$ 0	$ 0	$ 0.01
Earnings per share (in dollars per share)	$ 1.86	$ 1.72	$ 1.63
Earnings per average common share - diluted:
Income from continuing operations (in dollars per share)	$ 1.85	$ 1.72	$ 1.61
Income from discontinued operations (in dollars per share)	$ 0	$ 0	$ 0.01
Earnings per share (in dollars per share)	$ 1.85	$ 1.72	$ 1.62
Cash dividends declared per common share (in dollars per share)	$ 1.07	$ 1.03	$ 1.00