Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Operating Assets and Facilities ($123.2 and $123.3 related to a consolidated VIE)	$ 8,110.1	$ 7,390.7
Less: allowance for depreciation ($33.8 and $30.3 related to a consolidated VIE)	(2,425.5)	(2,320.4)
Nonrecourse ($18.1 and $25.4 related to a consolidated VIE)	(18.1)	(72.6)
Common stock, par value	$ 0.625	$ 0.625
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	66,575,685	66,349,906
Common stock, shares outstanding	44,173,551	45,868,698
Treasury stock, shares outstanding	22,402,134	20,481,208
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 ($33.8 and $30.3 related to a consolidated VIE)	(33.8)	(30.3)
Nonrecourse ($18.1 and $25.4 related to a consolidated VIE)	$ (18.1)	$ (25.4)