Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Operating Assets and Facilities ($123.2 and $123.3 related to a consolidated VIE)	$ 8,141.2	$ 8,143.5
Less: allowance for depreciation ($38.6 and $35.0 related to a consolidated VIE)	(2,487.9)	(2,455.5)
Nonrecourse ($9.2 and $15.9 related to a consolidated VIE)	$ (9.2)	$ (15.9)
Common stock, par value	$ 0.625	$ 0.625
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	66,729,691	66,600,984
Common stock, shares outstanding	42,371,254	44,198,850
Treasury stock, shares outstanding	24,358,437	22,402,134
Assets Held-for-sale, Long Lived, Fair Value Disclosure	$ 175.0	$ 7.0
Variable Interest Entity, Primary Beneficiary [Member]
Operating Assets and Facilities ($123.2 and $123.3 related to a consolidated VIE)	123.1	123.1
Less: allowance for depreciation ($38.6 and $35.0 related to a consolidated VIE)	(38.6)	(35.0)
Nonrecourse ($9.2 and $15.9 related to a consolidated VIE)	$ (9.2)	$ (15.9)