Business Segments (Balance Sheet Information) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Reinsurance receivables	$ 5,822	$ 6,092
Insurance receivables	1,904	1,726
Deferred acquisition costs	584	552
Insurance reserves
Claim and claim adjustment expenses	24,007	24,303
Unearned premiums	3,478	3,250
Future policy benefits	10,352	9,810
Policyholders’ funds	167	191
CNA Specialty [Member]
Reinsurance receivables	837	852
Insurance receivables	711	670
Deferred acquisition costs	308	300
Insurance reserves
Claim and claim adjustment expenses	6,925	6,840
Unearned premiums	1,708	1,629
Future policy benefits
Policyholders’ funds	13	15
CNA Commercial [Member]
Reinsurance receivables	1,149	1,188
Insurance receivables	1,182	1,047
Deferred acquisition costs	276	252
Insurance reserves
Claim and claim adjustment expenses	11,316	11,509
Unearned premiums	1,626	1,480
Future policy benefits
Policyholders’ funds	13	10
Life and Group Non-Core [Member]
Reinsurance receivables	1,323	1,375
Insurance receivables	8	8
Deferred acquisition costs
Insurance reserves
Claim and claim adjustment expenses	2,901	2,825
Unearned premiums	145	141
Future policy benefits	10,352	9,810
Policyholders’ funds	141	166
Corporate and Other Non-Core [Member]
Reinsurance receivables	2,513	2,677
Insurance receivables	3	1
Deferred acquisition costs
Insurance reserves
Claim and claim adjustment expenses	2,865	3,129
Unearned premiums
Future policy benefits
Policyholders’ funds
Eliminations [Member]
Reinsurance receivables
Insurance receivables
Deferred acquisition costs
Insurance reserves
Claim and claim adjustment expenses
Unearned premiums	(1)
Future policy benefits
Policyholders’ funds