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	$	1,057	$	911	$	1,081	$	1,134
Operating income	196		161		290		176
Net income	129		108		218		133

	Quarter Ended
(Millions of Dollars)	March 31, 2019		June 30, 2019		Sept. 30, 2019		Dec. 31, 2019
Operating revenues	$	1,223	$	910	$	1,044	$	1,060
Operating income	210		163		284		200
Net income	139		102		204		133