Quaterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2018

Quartertly Financial Data [Abstract]

Quarterly financial data

Quarterly financial information for the years ended December 31, 2018 and 2017 are summarized as follows:

(Millions)	2018								2017
Quarters ended		12/31		9/30		6/30		3/31		12/31		9/30		6/30		3/31
Revenues	$	406	$	386	$	351	$	318	$	296	$	286	$	253	$	252
Pretax income		108		107		93		108		72		85		52		66
Net income (loss) (a)	$	61	$	109	$	88	$	129	$	(791)	$	72	$	57	$	59

Beginning with the fourth quarter of 2017, includes impact of the Tax Act (refer to Note 11).