Income Taxes (Effective Rate Reconciliation) (Details) (USD $)	3 Months Ended								12 Months Ended									2 Months Ended	12 Months Ended			0 Months Ended	12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Non-US	Dec. 31, 2012 Non-US	Dec. 31, 2011 Non-US	Dec. 31, 2013 SWEDEN	Dec. 31, 2012 SWEDEN	Dec. 31, 2011 SWEDEN	Dec. 31, 2013 Luxembourg	Dec. 31, 2013 Luxembourg	Dec. 31, 2012 Luxembourg	Dec. 31, 2011 Luxembourg	Jan. 02, 2013 Sirius Group SWEDEN	Dec. 31, 2012 Sirius Group SWEDEN	Dec. 31, 2013 Business Acquisition [Member]	Dec. 31, 2012 Business Acquisition [Member]	Dec. 31, 2011 Business Acquisition [Member]
Income Tax Contingency [Line Items]
U.S. statutory rate (as a percent)					35.00%
Tax (expense) benefit at the U.S. statutory rate									$ (120,700,000)	$ (92,000,000)	$ (34,300,000)
Differences in taxes resulting from:
Non-U.S. earnings, net of foreign taxes									82,900,000	43,000,000	6,200,000
Change in valuation allowance									(33,600,000)	(14,100,000)	128,200,000							(41,300,000)	(1,400,000)
Effective Income Tax Rate Reconciliation, Tax Contingency, Amount									(10,200,000)	(1,300,000)	4,300,000
Tax exempt interest and dividends									(3,200,000)	(3,100,000)	(2,900,000)
Effective Income Tax Rate Reconciliation, Deduction, Other, Amount									1,700,000	2,900,000	(200,000)
Tax rate change enacted															0	65,400,000	0		0	7,200,000	1,200,000
Other, net									(1,800,000)	2,200,000	1,300,000													5,300,000	5,100,000	0
Income tax (expense) benefit	(27,400,000)	(8,200,000)	600,000	(41,600,000)	101,000,000	(47,800,000)	(6,400,000)	(31,100,000)	(76,600,000)	15,700,000	110,000,000
Effective income tax																						22.00%	26.30%
Increase (Decrease) in Deferred Income Taxes																						65,400,000
Pre-tax loss	134,200,000	55,300,000	3,600,000	151,800,000	(50,800,000)	135,100,000	37,600,000	140,900,000	344,900,000	262,800,000	98,000,000	294,300,000	250,000,000	65,400,000
Tax Payments and Receipts
Net income tax payments to (receipts from) national governments, total									$ 13,900,000	$ 17,500,000	$ 12,500,000