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Significant Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Significant Transactions
Gain on sale of subsidiary - Essentia		$ 23.0	$ 0
Excess of FV of aquired net assets over cost - American Fuji		6.9
OneBeacon | Essentia
Significant Transactions
Gain on sale of subsidiary - Essentia		23.0
Gain on sale of Essentia, after tax		15.0
Premiums written	$ 52.5		$ 145.8
Premiums written, percentage			15.70%

X

- Definition

Net of tax amount of gain (loss) classified as extraordinary item, including amount attributable to noncontrolling interests.

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- Definition

Amount of gain (loss) on sale or disposal of equity in securities of subsidiaries.

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- Definition

Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums written.

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Premiums Written, Percentage of Total

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