Income Taxes - Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Unrecognized Tax Benefits [Roll Forward]
Beginning Balance	$ 532.3	$ 567.4	$ 362.0
Additions based on tax positions related to the current year	9.5	4.2	8.8
Additions for tax positions of prior years	3.3	2.0	224.2
Reductions for tax positions for prior years	(203.7)	(36.4)	(26.5)
Settlements	(7.9)	0	0
Expiration of statutes	(0.1)	(4.9)	(1.1)
Ending Balance	$ 333.4	$ 532.3	$ 567.4