Investments (Narrative) (Details) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended		12 Months Ended
	Sep. 30, 2011 USD ($)	Jun. 30, 2011 USD ($)	Jun. 30, 2010 USD ($)	Jun. 30, 2011 USD ($)	Jun. 30, 2010 USD ($)	Dec. 31, 2010 USD ($)	Jul. 14, 2011 GBP (£)
Investments
Net unrealized gains impaired securities				$ 32.3		$ 36.1
Other-than-temporary impairments		0.5		1.7
Net other-than-temporary impairment losses on securities recognized in earnings		0.8	3.4	2.2	6.1
Amount transferred from unrealized losses in accumulated other comprehensive income		0.3		0.5
Derivative, loss on derivative	6.6			4.7
Fair value of the derivative liability		4.7		4.7
Notional amount of derivative contract							297.9
Loss on cash flow hedging activities		1.9		1.9
Cash flow hedge loss reclassified to earnings				0.2
Cash flow hedge loss reclassified to earnings, period				12
Derivative, collateral, obligation to return cash		5.1		5.1
Fixed maturities and equity securities		2.8		3.3
Derivative instruments, gain (loss) reclassification from accumulated OCI to income, estimated net amount to be transferred		$ 0.6		$ 2.8