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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ 24	$ (5)	$ 49	$ (31)
CNA Specialty [Member]
Medical Professional Liability	1	(17)	2	(20)
Other Professional Liability and Management Liability	(58)	(23)	(64)	(24)
Surety		1	1	2
Warranty
Other	2	(2)	4	(14)
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (55)	$ (41)	$ (57)	$ (56)