Summarized Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2020

Quarterly Financial Information Disclosure [Abstract]

Summarized Quarterly Financial Data (Unaudited)

	Quarter Ended
(Millions of Dollars)	March 31, 2020		June 30, 2020		Sept. 30, 2020		Dec. 31, 2020
Operating revenues	$	395	$	423	$	615	$	437
Operating income	53		80		163		63
Net income	43		72		127		53

	Quarter Ended
(Millions of Dollars)	March 31, 2019		June 30, 2019		Sept. 30, 2019		Dec. 31, 2019
Operating revenues	$	454	$	411	$	533	$	428
Operating income	75		82		135		55
Net income	54		59		105		45