Regulatory Assets and Liabilities (Details 1) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 879.1	$ 868.3
Deferred cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	724.5	725.0
Escrowed Bad Debt Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	64.6	81.1
Other, net [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 90.0	$ 62.2