CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues
Earned premiums	$ 1,015.5	$ 1,403.9	$ 1,858.8
Net investment income	71.4	96.6	125.5
Net realized and unrealized investment gains	10.6	74.6	248.6
Net other (expenses) revenues	(10.7)	9.6	23.1
Total revenues	1,086.8	1,584.7	2,256.0
Expenses
Loss and LAE	580.9	858.2	1,005.3
Policy acquisition expenses	219.0	311.6	376.3
Other underwriting expenses	173.3	233.1	308.5
General and administrative expenses	9.8	13.0	13.1
Interest expense on debt	20.5	29.6	39.7
Accretion of fair value adjustment to loss and LAE reserves			5.4
Total expenses	1,003.5	1,445.5	1,748.3
Pre-tax income from continuing operations	83.3	139.2	507.7
Income tax expense	(2.1)	(12.4)	(130.6)
Net income from continuing operations	81.2	126.8	377.1
Loss from discontinued operations, net of tax	(5.9)	(6.9)	(33.0)
Loss from sale of discontinued operations, net of tax	(19.2)
Net income including noncontrolling interests	56.1	119.9	344.1
Less: Net income attributable to noncontrolling interests	(1.0)	(1.6)	(2.1)
Net income attributable to OneBeacon's common shareholders	55.1	118.3	342.0
Change in foreign currency translation		0.7	(0.1)
Change in other comprehensive income and loss items	(11.2)	5.8	18.9
Comprehensive income attributable to OneBeacon's common shareholders	$ 43.9	$ 124.8	$ 360.8
Earnings (loss) per share attributable to OneBeacon's common shareholders-basic and diluted
Net income from continuing operations per share (in dollars per share)	$ 0.86	$ 1.34	$ 3.97
Loss from discontinued operations, net of tax, per share (in dollars per share)	$ (0.06)	$ (0.07)	$ (0.35)
Loss from sale of discontinued operations, net of tax, per share (in dollars per share)	$ (0.20)
Net income attributable to OneBeacon's common shareholders per share (in dollars per share)	$ 0.58	$ 1.25	$ 3.60
Dividends declared and paid per OneBeacon's common share (in dollars per share)	$ 1.84	$ 3.34	$ 0.84