Common Equity (Tables)

3 Months Ended

Mar. 31, 2018

Equity [Abstract]

Calculation of Basic and Diluted Earnings Per Share

	Three Months Ended March 31,
(in millions, except per share data)	2018		2017
Basic earnings per common share:
Net income available to common shareholders	$	47.6	$	22.6
Weighted average common shares issued and outstanding	176.9		156.4
Basic earnings per common share	$	0.27	$	0.14
Diluted earnings per common share:
Net income applicable to diluted earnings per common share	$	47.6	$	22.6
Dilutive potential common shares:
Restricted share units	0.3		0.4
Dilutive potential common shares	0.3		0.4
Total diluted average common shares issued and outstanding	177.2		156.8
Diluted earnings per common share	$	0.27	$	0.14