Financing Arrangements (Details 1) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Long-term debt
Total Long-term debt	$ 465.1	$ 464.7
Current portion of long-term debt	9.8	9.6
Long-term debt	455.3	455.1
Series A Medium Term Note [Member]
Long-term debt
Total Long-term debt	175.0	175.0
Senior Unsecured Notes [Member]
Long-term debt
Total Long-term debt	249.9	249.9
Ohio Water Development Revenue Refunding Bonds [Member]
Long-term debt
Total Long-term debt	12.2	12.2
Ohio Air Quality Development Revenue Refunding Bonds [Member]
Long-term debt
Total Long-term debt	9.5	9.5
Ohio Pollution Control Revenue Refunding Bonds [Member]
Long-term debt
Total Long-term debt	8.5	8.5
Other Long Term Debt [Member]
Long-term debt
Total Long-term debt	$ 10.0	$ 9.6