Debt (Junior Convertible Subordinated Debentures) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified			3 Months Ended	6 Months Ended	12 Months Ended	3 Months Ended	6 Months Ended	24 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Junior Subordinated Debt [Member]	Jun. 30, 2012 Junior Subordinated Debt [Member]	Dec. 31, 1997 Junior Subordinated Debt [Member]	Sep. 30, 2012 Convertible Preferred Stock [Member]	Jun. 30, 2012 Convertible Preferred Stock [Member]	Dec. 31, 2005 Convertible Preferred Stock [Member]	Jul. 16, 2012 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
Preferred securities issued unconditionally guarantees							8.4
Percentage of liquidation preference payable when called							100.00%
Liquidation preference on preferred stock							$ 421.2
Maturity date of junior convertible subordinated debentures				Dec. 01, 2027
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	436.7	436.7
Junior Convertible Subordinated Debentures, Redemption Date, Actual			July 16, 2012
Convertible Preferred Securities, Redemption Date, Actual						July 16, 2012
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
Junior Subordinated Debentures Owed to Unconsolidated Subsidiary, Issued					$ 515.5