Business Segments (Balance Sheet Information) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 4,850	$ 6,088
Insurance receivables	2,029	2,063
Deferred acquisition costs	627	624
Goodwill	154	155
Insurance reserves
Claim and claim adjustment expenses	23,475	24,089
Unearned premiums	3,703	3,718
Future policy benefits	8,890	10,471
Policyholders’ funds	27	116
CNA Specialty [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	636	546
Insurance receivables	799	775
Deferred acquisition costs	320	318
Goodwill	117	117
Insurance reserves
Claim and claim adjustment expenses	6,861	6,689
Unearned premiums	1,858	1,805
Future policy benefits
Policyholders’ funds	10	9
CNA Commercial [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	689	1,075
Insurance receivables	1,035	1,099
Deferred acquisition costs	253	257
Goodwill
Insurance reserves
Claim and claim adjustment expenses	10,156	10,649
Unearned premiums	1,466	1,536
Future policy benefits
Policyholders’ funds	17	15
Hardy [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	151	197
Insurance receivables	181	176
Deferred acquisition costs	54	49
Goodwill	37	38
Insurance reserves
Claim and claim adjustment expenses	380	386
Unearned premiums	249	249
Future policy benefits
Policyholders’ funds
Life and Group Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	549	1,203
Insurance receivables	12	11
Deferred acquisition costs
Goodwill
Insurance reserves
Claim and claim adjustment expenses	3,113	3,058
Unearned premiums	130	128
Future policy benefits	8,890	10,471
Policyholders’ funds		92
Corporate and Other Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	2,825	3,067
Insurance receivables	2	2
Deferred acquisition costs
Goodwill
Insurance reserves
Claim and claim adjustment expenses	2,965	3,307
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