CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
CONSOLIDATED BALANCE SHEETS
Accounts receivable and accrued unbilled revenues, reserves (in dollars)	$ 47.1	$ 41.9
Property, plant, and equipment, accumulated depreciation (in dollars)	$ 3,018.7	$ 2,900.2
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	78,287,906	77,781,685
Common stock, shares outstanding	77,904,935	77,350,079
Preferred stock of subsidiary, par value (in dollars per share)	$ 100	$ 100
Preferred stock of subsidiary, shares authorized	1,000,000	1,000,000
Preferred stock of subsidiary, shares issued	511,882	511,882
Preferred stock of subsidiary, shares outstanding	510,495	510,495