Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning Balance Accumulated Other Comprehensive Loss		$ (21.1)	$ (17.1)	$ (22.0)
Other Comprehensive Income (Loss) Before Reclassifications		(4.6)	(5.3)	4.6
Amounts Reclassified from Accumulated Other Comprehensive Loss		1.2	1.3	0.3
Net Other Comprehensive Income (Loss)		(3.4)	(4.0)	4.9
Ending Balance Accumulated Other Comprehensive Loss		(24.5)	(21.1)	(17.1)
Unrealized Gain (Loss) on Available-for-sale Securities [Member]
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning Balance Accumulated Other Comprehensive Loss		(0.3)	(0.1)	(0.1)
Other Comprehensive Income (Loss) Before Reclassifications		(0.4)	(0.3)	1.3
Amounts Reclassified from Accumulated Other Comprehensive Loss		(0.1)	0.1	(1.3)
Net Other Comprehensive Income (Loss)		(0.5)	(0.2)	0.0
Ending Balance Accumulated Other Comprehensive Loss		(0.8)	(0.3)	(0.1)
Defined Benefit Pension, Other Postretirement Items [Member]
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning Balance Accumulated Other Comprehensive Loss	[1]	(20.7)	(16.7)	(21.5)
Other Comprehensive Income (Loss) Before Reclassifications	[1]	(4.3)	(5.2)	3.2
Amounts Reclassified from Accumulated Other Comprehensive Loss	[1]	1.3	1.2	1.6
Net Other Comprehensive Income (Loss)	[1]	(3.0)	(4.0)	4.8
Ending Balance Accumulated Other Comprehensive Loss	[1]	(23.7)	(20.7)	(16.7)
Gains (Loss) on Cash Flow Hedge [Member]
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning Balance Accumulated Other Comprehensive Loss		(0.1)	(0.3)	(0.4)
Other Comprehensive Income (Loss) Before Reclassifications		0.1	0.2	0.1
Amounts Reclassified from Accumulated Other Comprehensive Loss		0.0	0.0	0.0
Net Other Comprehensive Income (Loss)		0.1	0.2	0.1
Ending Balance Accumulated Other Comprehensive Loss		$ 0.0	$ (0.1)	$ (0.3)

[1] Defined benefit pension and other postretirement items excluded from our Regulated Operations are recognized in accumulated other comprehensive loss and are subsequently reclassified out of accumulated other comprehensive loss as components of net periodic pension and other postretirement benefit expense. (See Note 17. Pension and Other Postretirement Benefit Plans.)