Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Changes in:
Net unrealized gains (losses) on investments with other-than-temporary impairments	$ 40	$ 38
Net unrealized gains (losses) on other investments	218	22
Net unrealized gains (losses) on investments	258	60
Foreign currency translation adjustment	21	25
Pension and postretirement benefits	6	1
Net unrealized gains (losses) on discontinued operations and other		1
Allocation to participating policyholders	(1)
Other comprehensive income (loss), net of tax	284	87
Net income (loss)	250	229
Comprehensive income (loss)	534	316
Change in:
Net unrealized (gains) losses on investments attributable to noncontrolling interests		2
Other comprehensive (income) loss attributable to noncontrolling interests		2
Net (income) loss attributable to noncontrolling interests		(9)
Comprehensive (income) loss attributable to noncontrolling interests		(7)
Total comprehensive income (loss) attributable to CNA	$ 534	$ 309