CONDENSED CONSOLIDATED BALANCE SHEETS CONDENSED CONSOLIDATED BALANCE SHEET (PARENTHETICAL) (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Accounts receivable and accrued unbilled revenues, reserves (in dollars)	$ 3.2	$ 2.5
Property, plant, and equipment, accumulated depreciation (in dollars)	$ 1,477.5	$ 1,336.0
Preferred stock, par value (in dollars per share)	$ 100
Preferred stock, shares authorized	1,000,000
Preferred stock, shares issued	511,882
Preferred stock, shares outstanding	511,882
Common stock, par value (in dollars per share)	$ 4
Common stock, shares authorized	32,000,000
Common stock, shares, issued	23,896,962
Common stock, shares outstanding	23,896,962