Income Taxes - Components of Income Tax Provision (Benefit) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Disclosure [Abstract]
Income Tax (Benefit)/Provision, Current, Federal	$ (72.0)	$ (1.0)	$ (215.1)
Income Tax (Benefit)/Provision, Current, State	5.6	(16.4)	(7.7)
Income Tax (Benefit)/Provision, Deferred, Federal	(726.7)	(450.6)	(221.9)
Income Tax (Benefit)/Provision, Deferred, State	(87.1)	(70.1)	(61.1)
Income Tax (Benefit)/Provision, Current, Ouside of the U.S.	13.0	8.7	10.4
Income Tax (Benefit)/Provision, Deferred, Ouside of the U.S.	(3.3)	(5.3)	2.9
Income Tax (Benefit)/Provision	$ (870.5)	$ (534.7)	$ (492.5)