Fair Value - Recurring Fair Value Measures, Activity in Level 3 (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Recurring Fair Value Measures, Activity in Level 3 [Line Items]
Fair Value Hierarchy Transfers, All Levels	$ 0	$ 0
Debt Securities Issued by the States of the United States (ARS) [Member]
Recurring Fair Value Measures, Activity in Level 3 [Line Items]
Balance as of December 31, 2011 and 2010, respectively	0	6.7
Redeemed During the Period	0	(6.7)	[1]
Balance as of June 30, 2012 and 2011, respectively	$ 0	$ 0

[1] The remaining ARS were redeemed at carrying value on January 5, 2011.