Document and Entity Information Document - shares	9 Months Ended
	Sep. 30, 2015	Oct. 30, 2015
Document and Entity Information [Abstract]
Entity Registrant Name	CNA FINANCIAL CORP
Entity Central Index Key	0000021175
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		270,260,625