Segments and Related Information (Tables)

12 Months Ended

Dec. 31, 2015

Segment Reporting [Abstract]

Results from Operations by Reportable Segment

(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

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other			Reconciling Eliminations			Consolidated Total
2013
Operating revenues (a)	$	3,081,171	$	1,080,703	$	40,754		$	—		$	4,202,628
Intersegment revenues	302		110		—			(412		)	—
Total revenues	$	3,081,473	$	1,080,813	$	40,754		$	(412	)	$	4,202,628
Depreciation and amortization	$	280,972	$	75,510	$	3,935		$	—		$	360,417
Interest charges and financing costs	129,787		30,604		554			—			160,945
Income tax expense (benefit)	220,356		42,294		(11,910		)	—			250,740
Net income	368,586		69,682		15,115			—			453,383

^(a)  Operating revenues include $13 million, $14 million and $13 million of intercompany revenue for the years ended Dec. 31, 2015, 2014 and 2013, respectively. See Note 16 for further discussion of related party transactions by reportable segment.