Property, Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment - Net	$ 2,576.5	$ 2,347.6
Asset Retirement Obligation [Roll Forward]
Beginning Obligation	77.9	57.0
Accretion Expense	4.6	3.8
Revisions in estimated cash flows	(0.7)	17.1
Ending Obligation	81.8	77.9
Regulated Utiity [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	3,380.0	3,232.9
Construction Work in Progress	303.9	151.8
Accumulated Depreciation	(1,181.7)	(1,102.8)
Property, Plant and Equipment - Net	2,502.2	2,281.9
Regulated Utiity [Member] | Generation Plant [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 to 35 years
Regulated Utiity [Member] | Transmission [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	42 to 61 years
Regulated Utiity [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	14 to 65 years
Non-Rate Base Energy Operations and Other Plant [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	131.3	118.0
Construction Work in Progress	3.4	4.2
Accumulated Depreciation	(60.4)	(56.7)
Property, Plant and Equipment - Net	74.3	65.5
Other Plant - Net	$ 0	$ 0.2
Non-Rate Base Energy Operations and Other Plant [Member] | Other Plant [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 to 25 years