Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2014
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Percent	(75.70%)
U.S. statutory rate (as a percent)	35.00%		35.00%
Income Tax Expense (Benefit)	$ (8.7)	$ 4.6
Equity in earnings of unconsolidated affiliates, net of tax	0.0	$ 7.3
Tax Assessment Year 2007 to 2009 [Member]
Income Tax Contingency [Line Items]
Income Tax Expense (Benefit)	12.8
Tax Years 2007, 2008, 2009 [Member] | OneBeacon [Member]
Income Tax Contingency [Line Items]
Income Tax Expense (Benefit)	12.8
Proceeds from Income Tax Refunds	6.0
Income Tax Credits and Adjustments	$ 4.7