Debt (Junior Convertible Subordinated Debentures) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended				3 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	24 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Jul. 15, 2012	Dec. 31, 2011	Sep. 30, 2012 Junior Subordinated Debt [Member]	Sep. 30, 2012 Junior Subordinated Debt [Member]	Dec. 31, 1997 Junior Subordinated Debt [Member]	Sep. 30, 2012 Convertible Preferred Stock [Member]	Dec. 31, 2005 Convertible Preferred Stock [Member]
Finance subsidiary ownership percentage								100.00%
Issued shares of convertible preferred securities										10.0
Convertible Preferred Securities, Dividend Rate, Percent										5.25%
Junior Convertible Subordinated Debt, Interest Rate, Stated Percentage							5.25%	5.25%
Preferred securities convertible into common stock										0.9865
Percentage of liquidation preference payable when called										100.00%
Liquidation preference on preferred stock										$ 421.2
Proceeds From Liquidation Of Investment In Unconsolidated Trust							15.5
Maturity date of junior convertible subordinated debentures								Dec. 01, 2027
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	0		0		436.7	436.7
Convertible Preferred Securities, Shares Repurchased											1.6
Convertible Preferred Securities, Shares Repurchased, Price Per Share											$ 45.27
Convertible Preferred Securities, Shares Repurchased, Amount											71.3
Incremental Debentures Issued to Unconsolidated Subsidary									15.5
Redemption Price As A Percentage Of Face Amount							100.00%
Junior Subordinated Debentures Owed to Unconsolidated Subsidiary, Issued									515.5
Gains (Losses) on Extinguishment of Debt	$ 6.8	$ 0	$ 6.8	$ 4.8			$ 6.0