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	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (118)	$ (205)	$ (423)
CNA Commercial [Member]
Commercial Auto	15	27	(98)
General Liability	59	(64)	(39)
Workers' Compensation	92	15	36
Property and Other	(62)	(24)	(103)
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ 104	$ (46)	$ (204)