Income Taxes (Effective Rate Reconciliation) (Details) (USD $)	3 Months Ended									12 Months Ended			0 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 02, 2013
Income Tax Contingency [Line Items]
U.S. statutory rate (as a percent)									35.00%
Tax (expense) benefit at the U.S. statutory rate										$ (105,600,000)	$ (120,700,000)	$ (92,000,000)
Differences in taxes resulting from:
Non-U.S. earnings, net of foreign taxes										77,700,000	82,900,000	43,000,000
Change in valuation allowance										(18,100,000)	(33,600,000)	(14,100,000)
Effective Income Tax Rate Reconciliation, Deduction, Other, Amount										(5,600,000)	(1,700,000)	(2,900,000)
Tax exempt interest and dividends										4,400,000	3,200,000	3,100,000
Tax reserve adjustments										(2,200,000)	(10,200,000)	(1,300,000)
Purchase of subsidiaries										(300,000)	5,300,000	5,100,000
Other, net										(3,600,000)	(1,800,000)	2,200,000
Income tax (expense) benefit	8,700,000	(7,800,000)	(23,900,000)	(30,300,000)	(27,400,000)	(8,200,000)	600,000	(41,600,000)		(53,300,000)	(76,600,000)	15,700,000
Pre-tax loss	46,200,000	34,400,000	109,000,000	112,100,000	134,200,000	55,300,000	3,600,000	151,800,000		301,700,000	344,900,000	262,800,000
Tax Payments and Receipts
Net income tax payments to (receipts from) national governments, total										9,400,000	13,900,000	17,500,000
Non-US
Differences in taxes resulting from:
Pre-tax loss										338,500,000	294,300,000	250,000,000
SWEDEN
Differences in taxes resulting from:
Tax rate change enacted										0	0	65,400,000
Luxembourg
Differences in taxes resulting from:
Change in valuation allowance									41,300,000	(1,200,000)	(1,400,000)
Tax rate change enacted										0	0	7,200,000
Sirius Group | SWEDEN
Differences in taxes resulting from:
Effective income tax												26.30%	22.00%
Increase (Decrease) in Deferred Income Taxes													$ 65,400,000