Summarized Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Summarized Quarterly Financial Data (Unaudited)

	Quarter Ended
(Millions of Dollars)	March 31, 2019		June 30, 2019		Sept. 30, 2019		Dec. 31, 2019
Operating revenues	$	454.1	$	410.5	$	533.1	$	428.1
Operating income	74.5		81.9		135.4		54.9
Net income	54.1		58.8		105.1		45.1

	Quarter Ended
(Millions of Dollars)	March 31, 2018		June 30, 2018		Sept. 30, 2018		Dec. 31, 2018
Operating revenues	$	447.2	$	481.3	$	540.1	$	464.6
Operating income (a)	57.1		87.6		111.0		56.0
Net income	33.1		58.5		81.5		40.2

^(a) 

In 2018, SPS implemented ASU No. 2017-07 related to net periodic benefit cost, which resulted in retrospective reclassification of pension costs from O&M expense to other income.