CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating revenues
Electric	$ 9,499,781	$ 9,275,986	$ 9,465,890
Natural gas	1,531,412	1,672,081	2,142,738
Other	75,727	76,419	77,507
Total operating revenues	11,106,920	11,024,486	11,686,135
Operating expenses
Electric fuel and purchased power	3,717,685	3,762,953	4,210,142
Cost of natural gas sold and transported	732,689	904,794	1,372,479
Cost of sales — other	36,075	36,216	34,352
Operating and maintenance expenses	2,326,558	2,329,670	2,334,379
Conservation and demand side management program expenses	244,784	224,679	301,772
Depreciation and amortization	1,303,203	1,124,524	1,019,045
Taxes (other than income taxes)	532,071	511,675	465,836
Loss on Monticello life cycle management/extended power uprate project	0	129,463	0
Total operating expenses	8,893,065	9,023,974	9,738,005
Operating income	2,213,855	2,000,512	1,948,130
Other income, net	7,950	5,400	5,296
Equity earnings of unconsolidated subsidiaries	42,123	34,390	30,151
Allowance for funds used during construction — equity	60,547	55,936	89,750
Interest charges and financing costs
Interest charges — includes other financing costs of $25,170, $24,175 and $22,986, respectively	646,907	595,282	566,608
Allowance for funds used during construction — debt	(27,028)	(26,248)	(38,402)
Total interest charges and financing costs	619,879	569,034	528,206
Income before income taxes	1,704,596	1,527,204	1,545,121
Income taxes	581,217	542,719	523,815
Net income	$ 1,123,379	$ 984,485	$ 1,021,306
Weighted average common shares outstanding:
Basic (in shares)	508,794	507,768	503,847
Diluted (in shares)	509,465	508,168	504,117
Earnings per average common share:
Basic (in dollars per share)	$ 2.21	$ 1.94	$ 2.03
Diluted (in dollars per share)	2.21	1.94	2.03
Cash dividends declared per common share (in dollars per share)	$ 1.36	$ 1.28	$ 1.20