Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Operating Assets and Facilities ($123.2 and $123.3 related to a consolidated VIE)	$ 8,341.3	$ 8,143.5
Less: allowance for depreciation ($37.4 and $35.0 related to a consolidated VIE)	(2,506.9)	(2,455.5)
Nonrecourse ($11.5 and $15.9 related to a consolidated VIE)	$ (11.5)	$ (15.9)
Common stock, par value	$ 0.625	$ 0.625
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	66,727,318	66,600,984
Common stock, shares outstanding	43,218,915	44,198,850
Treasury stock, shares outstanding	23,508,403	22,402,134
Variable Interest Entity, Primary Beneficiary [Member]
Operating Assets and Facilities ($123.2 and $123.3 related to a consolidated VIE)	$ 123.0	$ 123.1
Less: allowance for depreciation ($37.4 and $35.0 related to a consolidated VIE)	(37.4)	(35.0)
Nonrecourse ($11.5 and $15.9 related to a consolidated VIE)	$ (11.5)	$ (15.9)