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 from external customers	$	9,275,986	$	1,672,081	$	76,419		$	—		$	11,024,486
Intersegment revenues	1,511		1,251		—			(2,762		)	—
Total revenues	$	9,277,497	$	1,673,332	$	76,419		$	(2,762	)	$	11,024,486
Depreciation and amortization	$	962,565	$	154,892	$	7,067		$	—		$	1,124,524
Interest charges and financing costs	425,999		49,763		93,272			—			569,034
Income tax expense (benefit)	508,568		60,545		(26,394		)	—			542,719
Net income	921,403		106,023		(42,941		)	—			984,485

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other			Reconciling Eliminations			Consolidated Total
2014
Operating revenues from external customers	$	9,465,890	$	2,142,738	$	77,507		$	—		$	11,686,135
Intersegment revenues	1,774		5,893		—			(7,667		)	—
Total revenues	$	9,467,664	$	2,148,631	$	77,507		$	(7,667	)	$	11,686,135
Depreciation and amortization	$	866,746	$	144,661	$	7,638		$	—		$	1,019,045
Interest charges and financing costs	397,824		43,940		86,442			—			528,206
Income tax expense (benefit)	512,551		76,418		(65,154		)	—			523,815
Net income (loss)	890,535		128,559		2,212			—			1,021,306

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other			Reconciling Eliminations			Consolidated Total
2013
Operating revenues from external customers	$	9,034,045	$	1,804,679	$	76,198		$	—		$	10,914,922
Intersegment revenues	1,332		2,717		—			(4,049		)	—
Total revenues	$	9,035,377	$	1,807,396	$	76,198		$	(4,049	)	$	10,914,922
Depreciation and amortization	$	840,833	$	128,186	$	8,844		$	—		$	977,863
Interest charges and financing costs	386,198		44,927		104,895			—			536,020
Income tax expense (benefit)	495,044		25,543		(36,611		)	—			483,976
Net income (loss)	850,572		123,702		(26,040		)	—			948,234