Income Taxes - Rollforward of Gross Consolidated Liability for Unrecognized Income Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning of year	$ 196.8	$ 230.3	$ 197.1
Tax positions related to current year:
Additions	24.7	42.0	47.6
Reductions	(1.1)	(1.8)	0
Tax positions related to prior years:
Additions	64.4	14.0	23.7
Reductions	(3.9)	(71.0)	(20.2)
Settlements	(0.3)	(3.3)	(5.0)
Lapses in statutes of limitations	(10.7)	(13.4)	(12.9)
Unrecognized tax benefits, end of year	$ 269.9	$ 196.8	$ 230.3