Business Segments (Revenues by Line of Business) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Revenues	$ 2,463	$ 2,455
CNA Specialty [Domain]
Revenues	979	956
International - Specialty [Member]
Revenues	64	59
Management & Professional Liability [Member]
Revenues	704	700
Surety [Member]
Revenues	122	116
Warranty & Alternative Risks [Member]
Revenues	89	81
CNA Commercial [Domain]
Revenues	1,041	1,101
Commercial Insurance [Member]
Revenues	762	826
International - Commercial [Member]
Revenues	95	93
Small Business [Member]
Revenues	184	182
Hardy [Domain]
Revenues	100	67
Life and Group Non-Core [Member]
Revenues	331	315
Corporate and Other Non-Core [Member]
Revenues	13	17
Eliminations [Member]
Revenues	$ (1)	$ (1)