Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Loss	$ (16.8)		$ (21.6)		$ (17.1)	$ (22.0)
Other Comprehensive Income (Loss) Before Reclassifications	0		(2.3)
Amounts Reclassified From Accumulated Other Comprehensive Income (Loss)	0.3		2.7
Net Other Comprehensive Income	0.3		0.4
Reclassifications Out of Accumulated Other Comprehensive Income [Abstract]
AOCI Reclassification, Amortization of Defined Benefit Pension and Other Postretirement Items, Before Tax	(0.5)		(5.2)
Other Income (Expense) - Other [Member]
Reclassifications Out of Accumulated Other Comprehensive Income [Abstract]
AOCI Reclassification, Unrealized Gains on Available-for-sale Securities, Before Tax	0	[1]	0.8	[1]
Income Tax Expense [Member]
Reclassifications Out of Accumulated Other Comprehensive Income [Abstract]
AOCI Reclassification, Unrealized Gains on Available-for-sale Securities, Tax	0	[2]	(0.3)	[2]
AOCI Reclassification, Amortization of Defined Benefit Pension and Other Postretirement Items, Tax	0.2	[2]	2.0	[2]
Operating Expenses - Operating and Maintenance [Member]
Reclassifications Out of Accumulated Other Comprehensive Income [Abstract]
AOCI Reclassification, Amortization of Pension and Other Postretirement Items, Prior Service Costs, Before Tax	0.1	[3]	0.5	[3]
AOCI Reclassification, Amortization of Defined Benefit Pension and Other Postretirement Items, Actuarial Gains and Losses, Before Tax	(0.6)	[3]	(5.7)	[3]
Unrealized Gains and Losses on Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Loss	(0.1)		(0.1)		(0.1)	(0.1)
Other Comprehensive Income (Loss) Before Reclassifications	0		0.5
Amounts Reclassified From Accumulated Other Comprehensive Income (Loss)	0		(0.5)
Net Other Comprehensive Income	0		0
Defined Benefit Pension and Other Postretirement Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Loss	(16.4)		(21.2)		(16.7)	(21.5)
Other Comprehensive Income (Loss) Before Reclassifications	0		(2.9)
Amounts Reclassified From Accumulated Other Comprehensive Income (Loss)	0.3		3.2
Net Other Comprehensive Income	0.3		0.3
Gains and Losses on Cash Flow Hedge [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Loss	(0.3)		(0.3)		(0.3)	(0.4)
Other Comprehensive Income (Loss) Before Reclassifications	0		0.1
Amounts Reclassified From Accumulated Other Comprehensive Income (Loss)	0		0
Net Other Comprehensive Income	$ 0		$ 0.1

[1] Included in Other Income (Expense) – Other on the Consolidated Statement of Income.

[2] Included in Income Tax Expense on the Consolidated Statement of Income.

[3] Defined benefit pension and other postretirement benefit 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 14. Pension and Other Postretirement Benefit Plans)