Subsequent Events (Narrative) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	12 Months Ended
	Feb. 10, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Subsequent Event [Line Items]
Date of subsequent event	Feb. 10, 2014
Gross insurance reserves		$ 24,089	$ 24,763	$ 24,303	$ 25,496
Net income (loss) from continuing operations attributable to CNA		937	628	613
Majority of Run-off Annuity and Pension Deposit Business to be Sold [Member]
Subsequent Event [Line Items]
Gross insurance reserves		3,400
Net income (loss) from continuing operations attributable to CNA		31	8	(124)
Sale of Subsidiary Gain (Loss) [Member] | Majority of Run-off Annuity and Pension Deposit Business to be Sold [Member]
Subsequent Event [Line Items]
Expected impairment loss on sale, after-tax	$ 220