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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (26)	$ (81)	$ 23	$ (112)
CNA Specialty [Member]
Medical Professional Liability	13	9	15	(11)
Other Professional Liability and Management Liability	(9)	(4)	(73)	(28)
Surety	(79)	(76)	(78)	(74)
Warranty
Other	(7)	(3)	(3)	(17)
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (82)	$ (74)	$ (139)	$ (130)