Segment Information (Tables)

9 Months Ended

Sep. 30, 2016

Segment Reporting [Abstract]

Results from Operations by Reportable Segment

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas			All Other			Reconciling Eliminations			Consolidated Total
Three Months Ended Sept. 30, 2016
Operating revenues from external customers	$	2,799,964	$	221,956		$	18,227		$	—		$	3,040,147
Intersegment revenues	282		292			—			(574		)	—
Total revenues	$	2,800,246	$	222,248		$	18,227		$	(574	)	$	3,040,147
Net income (loss)	$	479,399	$	(5,297	)	$	(16,307	)	$	—		$	457,795

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas			All Other			Reconciling Eliminations			Consolidated Total
Three Months Ended Sept. 30, 2015
Operating revenues from external customers	$	2,667,480	$	216,019		$	17,813		$	—		$	2,901,312
Intersegment revenues	392		293			—			(685		)	—
Total revenues	$	2,667,872	$	216,312		$	17,813		$	(685	)	$	2,901,312
Net income (loss)	$	437,978	$	(4,176	)	$	(7,339	)	$	—		$	426,463

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other			Reconciling Eliminations			Consolidated Total
Nine Months Ended Sept. 30, 2016
Operating revenues from external customers	$	7,209,225	$	1,046,544	$	56,500		$	—		$	8,312,269
Intersegment revenues	1,038		820		—			(1,858		)	—
Total revenues	$	7,210,263	$	1,047,364	$	56,500		$	(1,858	)	$	8,312,269
Net income (loss)	$	863,076	$	84,974	$	(52,148	)	$	—		$	895,902

(Thousands of Dollars)	Regulated Electric			Regulated Natural Gas		All Other			Reconciling Eliminations			Consolidated Total
Nine Months Ended Sept. 30, 2015
Operating revenues from external customers	$	7,105,803		$	1,216,146	$	56,716		$	—		$	8,378,665
Intersegment revenues	1,142			1,141		—			(2,283		)	—
Total revenues	$	7,106,945		$	1,217,287	$	56,716		$	(2,283	)	$	8,378,665
Net income (loss)	$	733,954	(a)	$	72,617	$	(31,111	)	$	—		$	775,460

^(a)  Includes a net of tax charge related to the Monticello LCM/EPU project.  See Note 5.