Significant Transactions Sale of Essentia (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			3 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 Essentia OneBeacon	Dec. 31, 2012 Underwriting Agreement [Member] Essentia OneBeacon	Dec. 31, 2011 Underwriting Agreement [Member] Essentia OneBeacon
Unusual or Infrequent Item [Line Items]
Gain (Loss) on Disposition of Stock in Subsidiary	$ 21.3	$ 0	$ 0	$ 23.0
Gain (Loss) on Disposition of Stock in Subsidiary, After Tax				15.0
Premiums Written, Net					$ 179.7	$ 166.6
Premiums written, percentage of total					8.00%	8.00%