Income Taxes (Net Operating and Capital Loss Carryforwards) (Details) (USD $)	12 Months Ended				3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 UNITED STATES	Dec. 31, 2012 Sirius Re Holdings Inc.	Dec. 31, 2013 Sirius Re Holdings Inc.	Dec. 31, 2013 Expected to be utilized [Member] Luxembourg	Dec. 31, 2013 Subject to annual limitations [Member] UNITED STATES	Dec. 31, 2013 Operating and Capital Loss Carryforward	Dec. 31, 2013 Operating and Capital Loss Carryforward UNITED STATES	Dec. 31, 2013 Operating and Capital Loss Carryforward Luxembourg	Dec. 31, 2013 Operating and Capital Loss Carryforward SWEDEN	Dec. 31, 2013 Operating and Capital Loss Carryforward UNITED KINGDOM	Dec. 31, 2013 Operating and Capital Loss Carryforward NETHERLANDS	Dec. 31, 2013 Operating and Capital Loss Carryforward 2013 [Member]	Dec. 31, 2013 Operating and Capital Loss Carryforward 2013 [Member] UNITED STATES	Dec. 31, 2013 Operating and Capital Loss Carryforward 2013 [Member] Luxembourg	Dec. 31, 2013 Operating and Capital Loss Carryforward 2013 [Member] SWEDEN	Dec. 31, 2013 Operating and Capital Loss Carryforward 2013 [Member] UNITED KINGDOM	Dec. 31, 2013 Operating and Capital Loss Carryforward 2013 [Member] NETHERLANDS	Dec. 31, 2013 Operating and Capital Loss Carryforward 2014-2018 [Member]	Dec. 31, 2013 Operating and Capital Loss Carryforward 2014-2018 [Member] UNITED STATES	Dec. 31, 2013 Operating and Capital Loss Carryforward 2014-2018 [Member] Luxembourg	Dec. 31, 2013 Operating and Capital Loss Carryforward 2014-2018 [Member] SWEDEN	Dec. 31, 2013 Operating and Capital Loss Carryforward 2014-2018 [Member] UNITED KINGDOM	Dec. 31, 2013 Operating and Capital Loss Carryforward 2014-2018 [Member] NETHERLANDS	Dec. 31, 2013 Operating and Capital Loss Carryforward 2019-2013 [Member]	Dec. 31, 2013 Operating and Capital Loss Carryforward 2019-2013 [Member] UNITED STATES	Dec. 31, 2013 Operating and Capital Loss Carryforward 2019-2013 [Member] Luxembourg	Dec. 31, 2013 Operating and Capital Loss Carryforward 2019-2013 [Member] SWEDEN	Dec. 31, 2013 Operating and Capital Loss Carryforward 2019-2013 [Member] UNITED KINGDOM	Dec. 31, 2013 Operating and Capital Loss Carryforward 2019-2013 [Member] NETHERLANDS	Dec. 31, 2013 Operating and Capital Loss Carryforward 2024-2033 [Member]	Dec. 31, 2013 Operating and Capital Loss Carryforward 2024-2033 [Member] UNITED STATES	Dec. 31, 2013 Operating and Capital Loss Carryforward 2024-2033 [Member] Luxembourg	Dec. 31, 2013 Operating and Capital Loss Carryforward 2024-2033 [Member] SWEDEN	Dec. 31, 2013 Operating and Capital Loss Carryforward 2024-2033 [Member] UNITED KINGDOM	Dec. 31, 2013 Operating and Capital Loss Carryforward 2024-2033 [Member] NETHERLANDS	Dec. 31, 2013 Operating and Capital Loss Carryforward No expiration date [Member]	Dec. 31, 2013 Operating and Capital Loss Carryforward No expiration date [Member] UNITED STATES	Dec. 31, 2013 Operating and Capital Loss Carryforward No expiration date [Member] Luxembourg	Dec. 31, 2013 Operating and Capital Loss Carryforward No expiration date [Member] SWEDEN	Dec. 31, 2013 Operating and Capital Loss Carryforward No expiration date [Member] UNITED KINGDOM	Dec. 31, 2013 Operating and Capital Loss Carryforward No expiration date [Member] NETHERLANDS
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon
Operating Loss Carryforwards							$ 1,284,100,000	$ 18,200,000	$ 2,270,000,000	$ 441,000,000	$ 1,750,000,000	$ 62,300,000	$ 15,600,000	$ 1,100,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 500,000	$ 0	$ 0	$ 0	$ 0	$ 500,000	$ 11,800,000	$ 11,200,000	$ 0	$ 0	$ 0	$ 600,000	$ 429,800,000	$ 429,800,000	$ 0	$ 0	$ 0	$ 0	$ 1,827,900,000	$ 0	$ 1,750,000,000	$ 62,300,000	$ 15,600,000	$ 0
Net deferred tax assets
Gross deferred tax asset									669,200,000	148,600,000	511,300,000	5,800,000	3,200,000	300,000
Valuation allowance									(254,300,000)	(58,300,000)	(195,700,000)	0	0	(300,000)
Total net deferred income tax assets	617,600,000	697,100,000							414,900,000	90,300,000	315,600,000	5,800,000	3,200,000	0
Foreign tax credit carryforwards, subject to expiration				11,600,000		5,200,000
Valuation allowance	33,600,000	14,100,000	(128,200,000)		3,900,000
Alternative minimum tax credit carryforwards, not subject to expiration	$ 11,500,000