Segments and Related Information (Tables)

12 Months Ended

Dec. 31, 2016

Segment Reporting [Abstract]

Results from Operations by Reportable Segment

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other			Reconciling Eliminations			Consolidated Total
2016
Operating revenues (a)	$	3,049,352	$	957,721	$	40,723		$	—		$	4,047,796
Intersegment revenues	275		110		—			(385		)	—
Total revenues	$	3,049,627	$	957,831	$	40,723		$	(385	)	$	4,047,796
Depreciation and amortization	$	337,583	$	101,663	$	4,309		$	—		$	443,555
Interest charges and financing costs	136,274		37,881		431			—			174,586
Income tax expense (benefit)	228,825		45,960		(867		)	—			273,918
Net income	383,973		75,426		4,092			—			463,491

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other			Reconciling Eliminations			Consolidated Total
2015
Operating revenues (a)	$	3,115,257	$	1,006,666	$	41,590		$	—		$	4,163,513
Intersegment revenues	301		67		—			(368		)	—
Total revenues	$	3,115,558	$	1,006,733	$	41,590		$	(368	)	$	4,163,513
Depreciation and amortization	$	311,122	$	96,384	$	4,161		$	—		$	411,667
Interest charges and financing costs	136,397		34,935		576			—			171,908
Income tax expense (benefit)	234,873		44,192		(625		)	—			278,440
Net income	391,257		74,267		1,278			—			466,802

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other			Reconciling Eliminations			Consolidated Total
2014
Operating revenues (a)	$	3,125,937	$	1,215,324	$	41,888		$	—		$	4,383,149
Intersegment revenues	339		180		—			(519		)	—
Total revenues	$	3,126,276	$	1,215,504	$	41,888		$	(519	)	$	4,383,149
Depreciation and amortization	$	285,968	$	89,186	$	4,048		$	—		$	379,202
Interest charges and financing costs	124,118		29,987		535			—			154,640
Income tax expense (benefit)	208,095		50,874		(15,378		)	—			243,591
Net income	349,793		84,324		21,071			—			455,188

^(a)  Operating revenues include $13 million, $13 million and $14 million of intercompany revenue for the years ended Dec. 31, 2016, 2015 and 2014, respectively. See Note 16 for further discussion of related party transactions by reportable segment.