Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Changes in:
Net unrealized gains (losses) on investments with other-than-temporary impairments	$ 36	$ (14)	$ 73	$ 25
Net unrealized gains (losses) on other investments	191	236	530	558
Net unrealized gains (losses) on investments	227	222	603	583
Foreign currency translation adjustment	33	(52)	37	(22)
Pension and postretirement benefits	3	1	12	3
Net unrealized gains (losses) on discontinued operations and other				1
Allocation to participating policyholders		(6)	(2)	(7)
Other comprehensive income (loss), net of tax	263	165	650	558
Net income (loss)	221	76	637	434
Comprehensive income (loss)	484	241	1,287	992
Other comprehensive (income) loss attributable to noncontrolling interests related to changes in net unrealized (gains) losses on investments				(8)
Net (income) loss attributable to noncontrolling interests		(1)		(15)
Comprehensive (income) loss attributable to noncontrolling interests		(1)		(23)
Total comprehensive income (loss) attributable to CNA	$ 484	$ 240	$ 1,287	$ 969