Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Operating Assets and Facilities ($123.2 and $123.3 related to a consolidated VIE)	$ 8,091.4	$ 7,390.7
Less: allowance for depreciation ($32.6 and $30.3 related to a consolidated VIE)	(2,402.7)	(2,320.4)
Nonrecourse ($20.5 and $25.4 related to a consolidated VIE)	(20.5)	(72.6)
Common stock, par value	$ 0.625	$ 0.625
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	66,569,614	66,349,906
Common stock, shares outstanding	44,792,310	45,868,698
Treasury stock, shares outstanding	21,777,304	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 ($32.6 and $30.3 related to a consolidated VIE)	(32.6)	(30.3)
Nonrecourse ($20.5 and $25.4 related to a consolidated VIE)	$ (20.5)	$ (25.4)