CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Accounts receivable and accrued unbilled revenues, reserves (in dollars)	$ 65.5	$ 49.4
Property, plant, and equipment, accumulated depreciation (in dollars)	$ 3,363.8	$ 3,236.6
Common stock, par value (in dollars per share)	$ 1
Common stock, shares authorized	200,000,000
Common stock, shares issued	79,963,091	79,919,176
Common stock, shares outstanding	79,534,171	79,445,380
Preferred stock of subsidiary, par value (in dollars per share)	$ 100
Preferred stock of subsidiary, shares authorized	1,000,000
Preferred stock of subsidiary, shares issued	511,882
Preferred stock of subsidiary, shares outstanding	510,495