Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Operating Assets and Facilities ($123.2 and $123.3 related to a consolidated VIE)	$ 7,958.7	$ 7,390.7
Less: allowance for depreciation ($31.4 and $30.3 related to a consolidated VIE)	(2,358.9)	(2,320.4)
Nonrecourse ($23.0 and $25.4 related to a consolidated VIE)	(70.1)	(72.6)
Common stock, par value	$ 0.625	$ 0.625
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	66,529,703	66,349,906
Common stock, shares outstanding	46,048,495	45,868,698
Treasury stock, shares outstanding	20,481,208	20,118,120
Variable Interest Entity, Primary Beneficiary [Member]
Operating Assets and Facilities ($123.2 and $123.3 related to a consolidated VIE)	123.2	123.3
Less: allowance for depreciation ($31.4 and $30.3 related to a consolidated VIE)	(31.4)	(30.3)
Nonrecourse ($23.0 and $25.4 related to a consolidated VIE)	$ (23.0)	$ (25.4)