Business Segments (Balance Sheet Information) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 6,088	$ 6,231
Insurance receivables	2,063	1,983
Deferred acquisition costs	624	598
Goodwill	155	154
Insurance reserves
Claim and claim adjustment expenses	24,089	24,763
Unearned premiums	3,718	3,610
Future policy benefits	10,471	11,475
Policyholders’ funds	116	157
CNA Specialty [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	546	665
Insurance receivables	775	673
Deferred acquisition costs	318	300
Goodwill	117	117
Insurance reserves
Claim and claim adjustment expenses	6,689	6,748
Unearned premiums	1,805	1,685
Future policy benefits
Policyholders’ funds	9	8
CNA Commercial [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	1,075	1,155
Insurance receivables	1,099	1,116
Deferred acquisition costs	257	269
Goodwill
Insurance reserves
Claim and claim adjustment expenses	10,649	11,326
Unearned premiums	1,536	1,569
Future policy benefits
Policyholders’ funds	15	15
Hardy [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	197	294
Insurance receivables	176	181
Deferred acquisition costs	49	29
Goodwill	38	37
Insurance reserves
Claim and claim adjustment expenses	386	521
Unearned premiums	249	222
Future policy benefits
Policyholders’ funds
Life and Group Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	1,203	1,273
Insurance receivables	11	9
Deferred acquisition costs
Goodwill
Insurance reserves
Claim and claim adjustment expenses	3,058	3,006
Unearned premiums	128	134
Future policy benefits	10,471	11,475
Policyholders’ funds	92	134
Corporate and Other Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	3,067	2,844
Insurance receivables	2	4
Deferred acquisition costs
Goodwill
Insurance reserves
Claim and claim adjustment expenses	3,307	3,162
Unearned premiums
Future policy benefits
Policyholders’ funds
Eliminations [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables
Insurance receivables
Deferred acquisition costs
Goodwill
Insurance reserves
Claim and claim adjustment expenses
Unearned premiums
Future policy benefits
Policyholders’ funds