Investments (Narrative) (Details) In Millions	3 Months Ended		9 Months Ended		12 Months Ended		9 Months Ended
	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)	Dec. 31, 2010 USD ($)	Jul. 14, 2011 GBP (£)	Sep. 30, 2011 Treasury Lock Forward Agreement [Member] USD ($)
Gain (Loss) on Investments [Line Items]
Net unrealized gains on impaired securities			$ 26.2		$ 36.1
Other-than-temporary impairments	1.1	0.2	2.8
Net other-than-temporary impairment losses on securities recognized in earnings	1.5	1.4	3.7	7.5
Amount transferred from unrealized losses in accumulated other comprehensive income	0.4	1.2	0.9
Derivative, loss on derivative	6.6		11.3
Notional amount of foreign currency contract						297.9
Derivative instruments, gain recognized in income	6.5
Cash flow hedge loss reclassified into expense			0.2
OTTI of fixed maturities and equity securities				3.5
Derivative instruments, gain (loss) reclassification from accumulated OCI to income, estimated net amount to be transferred				4.0
Restricted assets, marketable securities	392.0		392.0
Restricted assets, cash and cash equivalents	99.0		99.0
Unrealized losses arising during period, Pre-Tax							$ 1.9