Business Segments (Balance Sheet Information) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Reinsurance receivables	$ 6,092	$ 7,204
Insurance receivables	1,726	1,717
Deferred acquisition costs	658	1,079
Insurance reserves
Claim and claim adjustment expenses	24,303	25,496
Unearned premiums	3,250	3,203
Future policy benefits	9,810	8,718
Policyholders’ funds	191	173
CNA Specialty [Member]
Reinsurance receivables	852	906
Insurance receivables	670	654
Deferred acquisition costs	347	330
Insurance reserves
Claim and claim adjustment expenses	6,840	6,793
Unearned premiums	1,629	1,543
Future policy benefits
Policyholders’ funds	15	16
CNA Commercial [Member]
Reinsurance receivables	1,188	1,973
Insurance receivables	1,047	1,050
Deferred acquisition costs	311	315
Insurance reserves
Claim and claim adjustment expenses	11,509	12,522
Unearned premiums	1,480	1,526
Future policy benefits
Policyholders’ funds	10	13
Life and Group Non-Core [Member]
Reinsurance receivables	1,375	1,502
Insurance receivables	8	9
Deferred acquisition costs		434
Insurance reserves
Claim and claim adjustment expenses	2,825	2,739
Unearned premiums	141	132
Future policy benefits	9,810	8,718
Policyholders’ funds	166	144
Corporate and Other Non-Core [Member]
Reinsurance receivables	2,677	2,823
Insurance receivables	1	4
Deferred acquisition costs
Insurance reserves
Claim and claim adjustment expenses	3,129	3,442
Unearned premiums		2
Future policy benefits
Policyholders’ funds
Eliminations [Member]
Reinsurance receivables
Insurance receivables
Deferred acquisition costs
Insurance reserves
Claim and claim adjustment expenses
Unearned premiums
Future policy benefits
Policyholders’ funds