Claim and Claim Adjustment Expense Reserves (Net prior year claim and allocated claim adjustment expense reserve development for CNA Commercial 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 Commercial [Member]
Commercial Auto	12	4	52	1
General Liability	39	(18)	64	(24)
Workers' Compensation	24	26	74	96
Property and Other	(18)	(15)	(37)	(60)
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ 57	$ (3)	$ 153	$ 13