Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued [Abstract]
Balance at beginning of period	$ 146.7	$ 160.5	$ 174.9
Increases as a result of tax positions taken during a prior year	5.3	4.6	7.8
Decreases as a result of tax positions taken during a prior year	(18.1)	(28.1)	(50.9)
Settlements with taxing authorities	(5.0)	(10.2)	0
Lapse of statutes of limitation	(0.2)	(0.6)	(5.0)
Increases as a result of tax positions taken during the current year	32.3	20.5	33.7
Balance at end of period	$ 161.0	$ 146.7	$ 160.5