Debt Senior Notes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			3 Months Ended				3 Months Ended				3 Months Ended	12 Months Ended					12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jun. 30, 2012 Senior Notes Six [Member]	Dec. 31, 2012 Senior Notes Six [Member]	Dec. 31, 2011 Senior Notes Six [Member]	Nov. 15, 2011 Senior Notes Six [Member]	Jun. 30, 2012 Senior Notes Seven [Member]	Dec. 31, 2012 Senior Notes Seven [Member]	Dec. 31, 2011 Senior Notes Seven [Member]	Nov. 15, 2011 Senior Notes Seven [Member]	Jun. 30, 2012 Senior Notes Six and Seven [Member]	Dec. 31, 2012 Senior Notes Six and Seven [Member]	Dec. 31, 2012 Senior Notes Three [Member]	Dec. 31, 2011 Senior Notes Three [Member]	Aug. 25, 2010 Senior Notes Three [Member]	Dec. 31, 2012 Senior Notes Five [Member]	Dec. 31, 2011 Senior Notes One Member	Dec. 31, 2012 Senior Notes One Member	Apr. 15, 2011 Senior Notes One Member
Debt Instrument [Line Items]
Redemption price of bonds as percentage of principal amount plus a make whole premium and any accrued unpaid interest to the redemption date	100.00%
Redemption Price Of Debt As Percentage Of The Principal Amount Of The Debentures upon change in control and credit rating decline	101.00%
Long-term Debt					$ (1,518.8)	$ (1,600.0)	$ (1,600.0)		$ (1,339.6)	$ (1,500.0)	$ (1,500.0)			$ (650.0)	$ (650.0)
Debt Instrument, Interest Rate, Stated Percentage					6.00%				6.25%					6.50%			6.875%		5.875%	5.875%
Aggregate Principal Outstanding Of Convertible Junior Subordinated Debentures																				218.1
Redemption Price Of Debt Instrument As Percentage Of Principal Amount Plus Make Whole Premium And Any Accrued Unpaid Interest To Redemption Date																				100.979%
Debt Instrument, Face Amount																650.0	650.0
Proceeds from Issuance of Senior Long-term Debt	0.8	4,101.4	1,150.0											641.9
Repayments of Long-term Debt				(81.2)				(160.0)
Gains (Losses) on Extinguishment of Debt												2.8	0.6	8.4
Write off of Deferred Debt Issuance Cost												$ 3.4						$ 1.7