CONDENSED CONSOLIDATED BALANCE SHEETS (PARENTHETICAL) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Accounts receivable and accrued unbilled revenues, reserves (in dollars)	$ 4.3	$ 2.5
Property, plant, and equipment, accumulated depreciation (in dollars)	$ 1,526.9	$ 1,483.1
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