CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY (USD $) In Millions, unless otherwise specified	Total	Common shareholders' equity	Common shares and paid-in surplus	Retained earnings	Accum. other comprehensive (loss) income, after tax	Noncontrolling interests, after tax	Comprehensive income (loss)
Balances at Dec. 31, 2010		$ 1,229.0	$ 1,000.5	$ 228.2	$ 0.3	$ 19.9
Increase (Decrease) in Stockholders' Equity
Net (loss) income	25.6	24.5		24.5		1.1	24.5
Amortization of restricted share and option awards		0.9	0.9
Issuance of common shares		0.3	0.3			0.3
Repurchases and retirements of common shares						(1.3)
Dividends		(154.8)		(154.8)		(0.9)
Contributions						0.1
Distributions						(5.0)
Other comprehensive (loss) income, after tax		0.3			0.3		0.3
Balances at Sep. 30, 2011		1,100.2	1,001.7	97.9	0.6	14.2
Balances at Dec. 31, 2011	1,113.9	1,099.8	1,002.2	108.5	(10.9)	14.1
Increase (Decrease) in Stockholders' Equity
Net (loss) income	(4.7)	(5.9)		(5.9)		1.2	(5.9)
Amortization of restricted share and option awards		1.9	1.9
Issuance of common shares		0.3	0.3			0.2
Dividends		(60.0)		(60.0)		(0.6)
Contributions						0.2
Gain on sale of OneBeacon Holdings (Luxembourg) S.a r.l.	(14.0)	14.0	14.0
Other comprehensive (loss) income, after tax		(1.7)			(1.7)		(1.7)
Balances at Sep. 30, 2012	$ 1,063.5	$ 1,048.4	$ 1,018.4	$ 42.6	$ (12.6)	$ 15.1