Quarterly Financial Information (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information (unaudited)

(in millions)	First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Total
2016
Operating revenues	$	975.5	$	877.2	$	1,023.8	$	916.3	$	3,792.8
Operating income	181.5		146.9		196.4		104.7		629.5
Net income attributed to common shareholder	107.3		82.6		115.2		59.2		364.3
2015
Operating revenues	$	1,084.6	$	883.0	$	981.1	$	905.4	$	3,854.1
Operating income	204.7		128.7		169.8		145.7		648.9
Net income attributed to common shareholder	121.4		74.6		100.1		79.6		375.7