Notes Payable and Debt and Financing Arrangements (Details) - Narrative (USD $)	9 Months Ended
Sep. 30, 2012
Debt Instrument [Line Items]
Aggregated required statutory capital and surplus for principal operating subsidiaries	$ 6,700,000,000
Percentage ownership of XLIT Ltd. and XL Capital Finance (Europe) plc	100.00%
March 2011 Credit Agreement [Member]
Debt Instrument [Line Items]
Line Of Credit Facility Optional Increased Capacity	500,000,000
December 2011 Credit Agreements [Member]
Debt Instrument [Line Items]
Line Of Credit Facility Optional Increased Capacity	500,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument Repurchased Face Amount	$ 600,000,000
Debt Instrument Interest Rate Stated Percentage	6.50%

Amount of statutory capital required to be maintained as of the balance sheet date under prescribed or permitted statutory accounting practices.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 60

-Paragraph 60

-Subparagraph h(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

Name:	us-gaap_StatutoryAccountingPracticesStatutoryCapitalAndSurplusRequired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant