Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Data [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

In the Company's opinion, the following quarterly financial data includes all adjustments, consisting of normal recurring adjustments, necessary to fairly present such amounts. Summarized consolidated quarterly unaudited financial data is as follows:

Quarter Ended (In millions, except per share data)		March 31		June 30		September 30		December 31		Total
Operating revenues	2019	$	490.0	$	513.7	$	755.4	$	472.5	$	2,231.6
	2018	$	492.7	$	567.0	$	698.8	$	511.8	$	2,270.3
Operating income	2019	$	49.7	$	110.0	$	274.3	$	70.3	$	504.3
	2018	$	66.6	$	137.7	$	227.3	$	58.0	$	489.6
Net income	2019	$	47.1	$	100.2	$	250.9	$	35.4	$	433.6
	2018	$	55.0	$	110.7	$	205.1	$	54.7	$	425.5
Basic earnings per average common share (A)	2019	$	0.24	$	0.50	$	1.25	$	0.18	$	2.17
	2018	$	0.28	$	0.55	$	1.03	$	0.27	$	2.13
Diluted earnings per average common share (A)	2019	$	0.24	$	0.50	$	1.25	$	0.18	$	2.16
	2018	$	0.27	$	0.55	$	1.02	$	0.27	$	2.12

(A)Due to the impact of dilution on the earnings per share calculation, quarterly earnings per share amounts may not add to the total.