Segment Information (Tables)

9 Months Ended

Sep. 30, 2013

Segment Reporting [Abstract]

Results from Continuing Operations by Reportable Segment

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Three Months Ended Sept. 30, 2013
Operating revenues from external customers	$	898,811	$	137,349	$	8,140	$	—		$	1,044,300
Intersegment revenues	67		3		—		(70		)	—
Total revenues	$	898,878	$	137,352	$	8,140	$	(70	)	$	1,044,300
Net income	$	158,498	$	3,555	$	4,213	$	—		$	166,266

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas			All Other		Reconciling Eliminations			Consolidated Total
Three Months Ended Sept. 30, 2012
Operating revenues from external customers	$	870,975	$	113,230		$	8,082	$	—		$	992,287
Intersegment revenues	63		(19		)	—		(44		)	—
Total revenues	$	871,038	$	113,211		$	8,082	$	(44	)	$	992,287
Net income	$	181,743	$	6,366		$	4,334	$	—		$	192,443

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Nine Months Ended Sept. 30, 2013
Operating revenues from external customers	$	2,368,041	$	730,569	$	29,576	$	—		$	3,128,186
Intersegment revenues	215		75		—		(290		)	—
Total revenues	$	2,368,256	$	730,644	$	29,576	$	(290	)	$	3,128,186
Net income	$	322,569	$	46,141	$	11,460	$	—		$	380,170

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Nine Months Ended Sept. 30, 2012
Operating revenues from external customers	$	2,267,905	$	643,632	$	26,303	$	—		$	2,937,840
Intersegment revenues	198		55		—		(253		)	—
Total revenues	$	2,268,103	$	643,687	$	26,303	$	(253	)	$	2,937,840
Net income	$	331,883	$	40,205	$	9,047	$	—		$	381,135