Investments - OTTI OCI (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other than Temporary Impairment, Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning	$ 19.4	$ 50.7	$ 46.0
Additional Credit Impairments [Abstract]
On securities not previously impaired	1.5	0.9	12.0
On securities previously impaired	3.7	6.7	11.7
Reductions [Abstract]
Securities intent impairments	0	(8.7)	(5.9)
Securities sold, matured, prepaid, or paid down	(4.6)	(30.2)	(13.1)
Balance, ending	$ 20.0	$ 19.4	$ 50.7

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

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This item represents reductions in the amount of cumulative losses recognized in earnings for other than temporary impairments (OTTI) for which a portion of the impairment had been recognized in other comprehensive income (a component of shareholders' equity) due to a change in status of the impaired security because of a change in the entity's intent to either sell the impaired security or it has become more likely than not that the entity will be required to sell the security before recovery of its cost basis.

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