CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating revenues
Electric	$ 9,275,986	$ 9,465,890	$ 9,034,045
Natural gas	1,672,081	2,142,738	1,804,679
Other	76,419	77,507	76,198
Total operating revenues	11,024,486	11,686,135	10,914,922
Operating expenses
Electric fuel and purchased power	3,762,953	4,210,142	4,018,672
Cost of natural gas sold and transported	904,794	1,372,479	1,082,751
Cost of sales — other	36,216	34,352	33,323
Operating and maintenance expenses	2,329,670	2,334,379	2,273,532
Conservation and demand side management program expenses	224,679	301,772	260,726
Depreciation and amortization	1,124,524	1,019,045	977,863
Taxes (other than income taxes)	511,675	465,836	420,500
Loss on Monticello life cycle management/extended power uprate project	129,463	0	0
Total operating expenses	9,023,974	9,738,005	9,067,367
Operating income	2,000,512	1,948,130	1,847,555
Other income, net	5,400	5,296	2,972
Equity earnings of unconsolidated subsidiaries	34,390	30,151	30,020
Allowance for funds used during construction — equity	55,936	89,750	87,683
Interest charges and financing costs
Interest charges — includes other financing costs of $24,175, $22,986 and $30,135, respectively	595,282	566,608	575,199
Allowance for funds used during construction — debt	(26,248)	(38,402)	(39,179)
Total interest charges and financing costs	569,034	528,206	536,020
Income before income taxes	1,527,204	1,545,121	1,432,210
Income taxes	542,719	523,815	483,976
Net income	$ 984,485	$ 1,021,306	$ 948,234
Weighted average common shares outstanding:
Basic (in shares)	507,768	503,847	496,073
Diluted (in shares)	508,168	504,117	496,532
Earnings per average common share:
Basic (in dollars per share)	$ 1.94	$ 2.03	$ 1.91
Diluted (in dollars per share)	1.94	2.03	1.91
Cash dividends declared per common share (in dollars per share)	$ 1.28	$ 1.20	$ 1.11