Document and Entity Information Document	3 Months Ended
	Mar. 31, 2013	Apr. 26, 2013
Entity Information [Line Items]
Entity Registrant Name	CNA FINANCIAL CORP
Entity Central Index Key	0000021175
Current Fiscal Year End Date	--03-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		269,684,313