Business Segments (Balance Sheet Information) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Reinsurance receivables	$ 5,099	$ 6,088
Insurance receivables	2,132	2,063
Deferred acquisition costs	652	624
Goodwill	155	155
Insurance reserves
Claim and claim adjustment expenses	23,933	24,089
Unearned premiums	3,838	3,718
Future policy benefits	8,254	10,471
Policyholders’ funds	26	116
CNA Specialty [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	555	546
Insurance receivables	794	775
Deferred acquisition costs	326	318
Goodwill	117	117
Insurance reserves
Claim and claim adjustment expenses	6,786	6,689
Unearned premiums	1,863	1,805
Future policy benefits
Policyholders’ funds	9	9
CNA Commercial [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	1,050	1,075
Insurance receivables	1,134	1,099
Deferred acquisition costs	273	257
Goodwill
Insurance reserves
Claim and claim adjustment expenses	10,574	10,649
Unearned premiums	1,583	1,536
Future policy benefits
Policyholders’ funds	17	15
Hardy [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	153	197
Insurance receivables	191	176
Deferred acquisition costs	53	49
Goodwill	38	38
Insurance reserves
Claim and claim adjustment expenses	377	386
Unearned premiums	250	249
Future policy benefits
Policyholders’ funds
Life and Group Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	401	1,203
Insurance receivables	10	11
Deferred acquisition costs
Goodwill
Insurance reserves
Claim and claim adjustment expenses	3,085	3,058
Unearned premiums	142	128
Future policy benefits	8,254	10,471
Policyholders’ funds		92
Corporate and Other Non-Core [Member]
Segment Reporting Information [Line Items]
Reinsurance receivables	2,940	3,067
Insurance receivables	3	2
Deferred acquisition costs
Goodwill
Insurance reserves
Claim and claim adjustment expenses	3,111	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