Document and Entity Information Document	9 Months Ended
	Sep. 30, 2011	Oct. 28, 2011
Document Information [Line Items]
Entity Registrant Name	CNA FINANCIAL CORP
Entity Central Index Key	0000021175
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		269,274,900