Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2012

Schedule of assets and liabilities measured on a recurring basis, at fair value

The major categories of assets and liabilities measured on a recurring basis, at fair value, as of September 30, 2012 and December 31, 2011, are as follows (in millions):

	September 30, 2012
	Level 1		Level 2		Level 3		Total
Treasury bills	$	246.3	$	—	$	—	$	246.3
Government agency securities	—		117.9		—		117.9
FDIC guaranteed corporate debt	—		28.2		—		28.2
Total	$	246.3	$	146.1	$	—	$	392.4

	December 31, 2011
	Level 1		Level 2		Level 3		Total
Treasury bills	$	90.2	$	—	$	—	$	90.2
FDIC guaranteed corporate debt	—		114.8		—		114.8
Government agency securities	—		169.8		—		169.8
Money market instruments	—		0.2		—		0.2
Total	$	90.2	$	284.8	$	—	$	375.0

The classification in the fair value table as of December 31, 2011 has been revised to conform to current period classifications due to an immaterial error related to previously disclosed fair value hierarchy tables.