Consolidated Statements of Comprehensive Income (Loss) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Changes in:
Net unrealized gains (losses) on investments with other-than-temporary impairments	$ 10	$ 86	$ (95)
Tax on net unrealized gains (losses) on investments with other-than-temporary impairments	(6)	(47)	52
Net unrealized gains (losses) on other investments	362	505	3,741
Tax on net unrealized gains (losses) on other investments	(198)	(269)	(2,024)
Net unrealized gains (losses) on investments	372	591	3,646
Tax on net unrealized gains (losses) on investments	204	316	1,972
Net unrealized gains (losses) on discontinued operations and other	(1)	9	9
Tax on net unrealized gains (losses) on discontinued operations and other		(2)	(2)
Foreign currency translation adjustment	(15)	49	117
Pension and postretirement benefits	(208)	35	15
Tax on pension and postretirement benefits	111	(18)	(8)
Allocation to participating policyholders	(7)	(23)	(40)
Other comprehensive income (loss), net of tax	141	661	3,747
Tax on other comprehensive income (loss)	(93)	(336)	(1,982)
Net income (loss)	630	758	481
Comprehensive income (loss)	771	1,419	4,228
Changes in:
Net unrealized (gains) losses on investments attributable to noncontrolling interests	(8)	(10)	(24)
Pension and postretirement benefit attributable to noncontrolling interests		(2)	(2)
Other comprehensive (income) loss attributable to noncontrolling interests	(8)	(12)	(26)
Net (income) loss attributable to noncontrolling interests	(16)	(68)	(62)
Comprehensive (income) loss attributable to noncontrolling interests	(24)	(80)	(88)
Total comprehensive income (loss) attributable to CNA	$ 747	$ 1,339	$ 4,140