Benefit Plans Part 2 (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2000
CNA Savings Plan [Abstract]
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.
Stock-Based Compensation [Abstract]
Share-based compensation arrangement by share-based payment award, number of shares authorized	6
Share-based compensation arrangement by share-based payment award, number of shares available for grant	1.9
Allocated share-based compensation expense	$ 9	$ 6	$ 5
Employee service share-based compensation, tax benefit from compensation expense	3	2	2
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized	12
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized, period for recognition	1 year 4 months 16 days
Share awards plan agreement	Share awards currently granted under the Plan include restricted shares, performance-based RSUs, and performance share units. Generally, restricted shares vest ratably over a four-year service period following the date of grant. Performance-based RSUs generally become payable within a range of 0% to 100% of the number of shares initially granted based upon the attainment of specific annual performance goals and vest ratably over a four-year service period following the date of grant. Performance share units become payable within a range of 0% to 200% of the number of shares initially granted based upon the attainment of specific performance goals achieved over a three year period.
Pension Plans, Defined Benefit [Member]
Defined benefit plan, estimated future employer contributions in next fiscal year	90
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined benefit plan, estimated future employer contributions in next fiscal year	6
Defined Contribution Pension [Member]
CNA Savings Plan [Abstract]
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.
Liability of the CNA Savings Plan included in Separate account liabilities and Policyholders' funds on the Consolidated Balance Sheets	256	381
Defined Contribution Plan, Cost Recognized	$ 70	$ 60	$ 61