Summary of Significant Accounting Policies (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Nov. 29, 2011
Percentage owned of outstanding common stock by majority shareholder	90.00%
Sale of CNA ownership percentage of FICOH				50.00%
Anticipated amounts due from insureds related to losses under deductible policies	$ 1,300,000,000	$ 1,400,000,000
Minimum interest rate used in determining present value of obligations of structured settlements not funded by annuities	7.10%	5.50%
Maximum interest rate used in determining present value of obligations of structured settlements not funded by annuities	9.70%	8.00%
Discounted reserves for unfunded structured settlements	602,000,000	632,000,000
Discounted reserves for unfunded structure settlements, discount amount	1,000,000,000	1,100,000,000
Minimum interest rate used to discount workers' compensation lifetime claim reserves and accident and health claim reserves	3.00%	3.00%
Maximum interest rate used to discount workers' compensation lifetime claim reserves and accident and health claim reserves	6.50%	6.50%
Discounted reserves for worker's compensation lifetime claim reserves and accident and health claim reserves	2,200,000,000	2,100,000,000
Discounted reserves for worker's compensation lifetime claim reserves and accident and health claim reserves, discount amount	837,000,000	520,000,000
Minimum interest rate used to calculate reserves for long term care products	5.00%	5.00%
Maximum interest rate used to calculate reserves for long term care products	7.40%	7.50%
Minimum interest rate used to calculate reserves for payout annuity contracts	5.00%	5.40%
Maximum interest rate used to calculate reserves for payout annuity contracts	8.70%	7.50%
Increase in insurance reserves due to unlocking actuarial assumptions related to payout annuity contracts	33,000,000	166,000,000
Liability balance for guaranty fund	143,000,000	152,000,000
Related assets for premium tax offsets included in other assets	2,000,000	2,000,000
Percentage of billed receivables compared to total reinsurance receivables	5% or less
Deposit assets	3,000,000	18,000,000
Deposit liabilities	125,000,000	123,000,000
Deferred acquistion costs, shadow adjustment	369,000,000	398,000,000
Investments in life settlement contracts	100,000,000	117,000,000
Increase in fair value recognized on life settlement contracts	11,000,000	5,000,000	10,000,000
Gain recognized on matured life settlement contracts	42,000,000	28,000,000	19,000,000
Increase (decrease) in policyholders' funds, pension deposit guarantee liability	(20,000,000)	18,000,000	(24,000,000)
Shadow adjustment, net of participating policyholders' interest and tax	789,000,000	572,000,000
Reduction of net unrealized gains on investments included in AOCI due to shadow adjustments	1,511,000,000	722,000,000
Requisite service period for stock-based compensation expense	4 years
Foreign currency transaction gain (loss), before tax	12,000,000	4,000,000	(19,000,000)
Finite-lived intangible assets, net	40,000,000
Indefinite-lived intangible assets (excluding goodwill)	73,000,000	16,000,000
Weighted average number diluted shares outstanding adjustment	417,000	290,000	380,000
Antidilutive securities excluded from computation of earnings per share, amount	730,000	1,100,000	1,200,000
Interest paid, net	170,000,000	175,000,000	145,000,000
Proceeds from income tax refunds	29,000,000		175,000,000
Income taxes paid		61,000,000
New Accounting Pronouncement or Change in Accounting Principle, Retrospective Application Impracticable	Due to the lack of available historical data related to certain accident and health contracts issued prior to January 1, 2004, a full retrospective application of the change in accounting guidance was impracticable.
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	(5,000,000)	(2,000,000)	1,000,000
Decrease in basic and diluted earnings per share	0.02	0.01
Decrease in Deferred Policy Acquisition Costs		106,000,000
Increase in deferred tax assets liabilities net		37,000,000
Increase in other net realized investment gains		2,000,000
Decrease in deferred policy acquisition cost amortization expense		234,000,000	219,000,000
Increase in other cost and expense, operating		242,000,000	219,000,000
Decrease in income tax expense		4,000,000	1,000,000
Changes in net cash provided by (used in) operating, investing and financing activities
Furniture and Fixtures [Member]
Property, Plant and Equipment, Useful Life	7 years
Office Equipment [Member]
Property, Plant and Equipment, Useful Life	5 years
Building and Building Improvements [Member]
Property, Plant and Equipment, Useful Life	50 years
Minimum [Member] | Software [Member]
Property, Plant and Equipment, Useful Life	3 years
Maximum [Member] | Software [Member]
Property, Plant and Equipment, Useful Life	5 years
Property and Casualty insurance core operations [Member] | Business [Member]
Number of Operating Segments	3
Life and Group Non-Core & Corporate and Other Non-Core operations [Member] | Business [Member]
Number of Operating Segments	2