Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Operating Assets and Facilities ($123.2 and $123.3 related to a consolidated VIE)	$ 8,440.4	$ 8,204.0
Less: allowance for depreciation ($40.8 and $39.7 related to a consolidated VIE)	(2,563.9)	(2,505.6)
Nonrecourse ($4.7 and $6.9 related to a consolidated VIE)	$ (4.7)	$ (6.9)
Common stock, par value	$ 0.625	$ 0.625
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	66,886,672	66,776,290
Common stock, shares outstanding	40,881,743	41,970,098
Treasury stock, shares outstanding	26,004,929	24,806,192
Assets Held-for-sale, Long Lived, Fair Value Disclosure	$ 70.6	$ 106.0
Variable Interest Entity, Primary Beneficiary [Member]
Operating Assets and Facilities ($123.2 and $123.3 related to a consolidated VIE)	122.6	122.9
Less: allowance for depreciation ($40.8 and $39.7 related to a consolidated VIE)	(40.8)	(39.7)
Nonrecourse ($4.7 and $6.9 related to a consolidated VIE)	$ (4.7)	$ (6.9)