Benefit Plans Part 1 (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2000	Dec. 31, 2011 Pension Plans, Defined Benefit [Member]	Dec. 31, 2010 Pension Plans, Defined Benefit [Member]	Dec. 31, 2011 Other Postretirement Benefit Plans, Defined Benefit [Member]	Dec. 31, 2010 Other Postretirement Benefit Plans, Defined Benefit [Member]	Dec. 31, 2009 Other Postretirement Benefit Plans, Defined Benefit [Member]	Dec. 31, 2011 Investment Contracts with Insurance Company [Member]	Dec. 31, 2010 Investment Contracts with Insurance Company [Member]	Dec. 31, 2011 Partnership Interest [Member] Pension Plans, Defined Benefit [Member]
Defined benefit plan, description of plan amendment						In November 2010, CNA announced a change in its postretirement benefits. The plan previously offered a maximum $10,000 non-contributory retiree life insurance benefit to participants who met certain eligibility requirements. The change eliminated this benefit for all active employees effective January 1, 2011, and for all retirees effective January 1, 2012.
Defined benefit plan, effect of plan amendment on accumulated benefit obligation						$ 60
Defined benefit plan, accumulated benefit obligation			2,932	2,715
Assumptions used in calculating assumed health care cost trend rate					The CNA Health and Group Benefits Program has limited its share of the health care trend rate to a cost-of-living adjustment of 4% per year. For all participants, the employer subsidy on health care costs will not increase by more than 4% per year.
Defined benefit plan, health care cost trend rate assumed for next fiscal year					4.00%	4.00%	4.00%
Defined benefit plan, effect of one percentage point increase in the assumed health care cost trend rate on accumulated postretirement benefit obligation
Defined benefit plan, effect of one percentage point decrease in the assumed health care cost trend rate on accumulated postretirement benefit obligation					3
Defined benefit plan, effect of one percentage point increase in the assumed health care cost trend rate on service and interest cost components
Defined benefit plan, effect of one percentage point decrease in the assumed health care cost trend rate on service and interest cost components
Future capital call commitments										27
Limited partnership equity related hedge fund strategy plan assets			53.00%
Limited partnership hedge fund multi strategy plan assets			36.00%
Limited partnership hedge fund strategy distressed investments plan assets			10.00%
Limited partnership hedge fund strategies fixed income			1.00%
Defined benefit plan, estimated future employer contributions in next fiscal year			86		6
Description of CNA Savings Plan	CNA sponsors savings plans, which are generally contributory plans that allow most employees to contribute a maximum of 20% of their eligible compensation, subject to certain limitations prescribed by the IRS. The Company contributes matching amounts to participants, amounting to 70% of the first 6% (35% of the first 6% in the first year of employment) of eligible compensation contributed by the employee. Employees vest in these contributions ratably over five years.
Contract value of investment contract, liability to benefit plan								381	363
Description of transition from CNA pension plan to postretirement plan		As noted above, during 2000, CCC employees were required to make a choice regarding their continued participation in CNA's defined benefit pension plan. Employees who elected to forgo earning additional benefits in the defined benefit pension plan and all employees hired by CCC on or after January 1, 2000 receive a Company contribution of 3% or 5% of their eligible compensation, depending on their age. In addition, these employees are eligible to receive additional discretionary contributions of up to 2% of eligible compensation and an additional Company match of up to 80% of the first 6% of eligible compensation contributed by the employee. These additional contributions are made at the discretion of management and are contributed to participant accounts in the first quarter of the year following management's determination of the discretionary amounts. Employees vest in these contributions ratably over five years.
Pension and other postretirement benefit expense					$ 60	$ 61	$ 59