Supplemental Quarterly Information (Tables)

12 Months Ended

Dec. 31, 2017

Supplemental Quarterly Information [Abstract]

Schedule of Supplemental Quarterly Information

(Millions of dollars except per share amounts)	First Quarter		Second Quarter	Third Quarter	Fourth Quarter	Year
Year ended December 31, 2017
Sales and other operating revenues	$	544.7	509.7	498.3	545.0	2,097.7
Income (loss) from continuing operations before     income taxes		154.9	(21.9)	(63.6)	2.4	71.8
Income (loss) from continuing operations		57.5	(17.3)	(66.3)	(284.8)	(310.9)
Net income (loss)		58.5	(17.6)	(65.9)	(286.8)	(311.8)
Income (loss) from continuing operations per     Common share
Basic		0.33	(0.10)	(0.38)	(1.65)	(1.81)
Diluted		0.33	(0.10)	(0.38)	(1.65)	(1.81)
Net income (loss) per Common share
Basic		0.34	(0.10)	(0.38)	(1.66)	(1.81)
Diluted		0.34	(0.10)	(0.38)	(1.66)	(1.81)
Cash dividend per Common share		0.25	0.25	0.25	0.25	1.00
Market price of Common Stock 1
High		32.18	28.71	27.43	31.98	32.18
Low		25.76	24.06	22.63	25.02	22.63
Year ended December 31, 2016
Sales and other operating revenues	$	429.1	411.2	486.3	483.0	1,809.6
Loss from continuing operations before     income taxes		(265.0)	(131.3)	(16.7)	(80.1)	(493.1)
Income (loss) from continuing operations		(199.5)	2.9	(14.6)	(62.8)	(274.0)
Net income (loss)		(198.8)	2.9	(16.2)	(63.9)	(276.0)
Income from continuing operations per     Common share
Basic		(1.16)	0.02	(0.08)	(0.36)	(1.59)
Diluted		(1.16)	0.02	(0.08)	(0.36)	(1.59)
Net income (loss) per Common share
Basic		(1.16)	0.02	(0.08)	(0.37)	(1.60)
Diluted		(1.16)	0.02	(0.08)	(0.37)	(1.60)
Cash dividend per Common share		0.35	0.35	0.25	0.25	1.20
Market price of Common Stock 1
High		26.69	36.24	32.66	34.30	36.24
Low		15.76	23.49	25.14	25.00	15.76