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, Income Tax Penalties and Interest Accrued [Abstract]
Balance at beginning of period	$ 161.0	$ 146.7	$ 160.5
Increases as a result of tax positions taken during a prior year	28.2	5.3	4.6
Decreases as a result of tax positions taken during a prior year	(6.8)	(18.1)	(28.1)
Settlements with taxing authorities	(0.7)	(5.0)	(10.2)
Lapse of statutes of limitation	(1.1)	(0.2)	(1.0)
Increases as a result of tax positions taken during the current year	14.0	32.3	20.5
Balance at end of period	$ 194.6	$ 161.0	$ 146.7