CONSOLIDATED STATEMENTS OF CHANGES IN COMMON STOCK EQUITY - USD ($) $ in Millions	Total	Dividend and Distribution Reinvestment and Share Purchase Plan	Registered Public Offering	Common Equity	Common Equity Dividend and Distribution Reinvestment and Share Purchase Plan	Common Equity Registered Public Offering	Retained Earnings
Beginning Balance at Dec. 31, 2014	$ 273.1			$ 234.7			$ 38.4
Net Income	26.3						26.3
Dividends	(19.6)						(19.6)
Shares Issued Under Stock Plans	1.5			1.5
Issuance of Common Shares	1.3			1.3
Ending Balance at Dec. 31, 2015	282.6			237.5			45.1
Net Income	27.1						27.1
Dividends	(20.0)						(20.0)
Shares Issued Under Stock Plans	1.9			1.9
Issuance of Common Shares	1.3			1.3
Ending Balance at Dec. 31, 2016	292.9			240.7			52.2
Net Income	29.0						29.0
Dividends	(20.4)						(20.4)
Shares Issued Under Stock Plans	2.1			2.1
Issuance of Common Shares		$ 1.3	$ 31.7		$ 1.3	$ 31.7
Ending Balance at Dec. 31, 2017	$ 336.6			$ 275.8			$ 60.8