Claim and Claim Adjustment Expense Reserves (Net prior year claim and allocated claim adjustment expense reserve development for CNA Specialty segment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ 25	$ (26)
CNA Specialty [Member]
Medical Professional Liability	1	(3)
Other Professional Liability and Management Liability	(6)	(1)
Surety	1	1
Warranty
Other	2	(12)
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (2)	$ (15)