Claim and Claim Adjustment Expense Reserves - Net Prior Year Development in CNA's Property and Casulaity Operations (Detail) - CNA Financial [Member] - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Medical professional liability	$ 3	$ 2	$ 23	$ 22
Other professional liability and management liability	(34)	(37)	(68)	(69)
Surety	(15)		(30)
Commercial auto		1	(1)	(25)
General liability	26	1	18	(17)
Workers' compensation	(6)	(47)	(12)	(47)
Other	(33)	25	(28)	24
Total pretax (favorable) unfavorable development	$ (59)	$ (55)	$ (98)	$ (112)

Net prior year claim and allocated claim adjustment.

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- Definition

Net Prior Year Claim and Allocated Claim Adjustment Expense, Medical Professional Liability

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Net Prior Year Claim and Allocated Claim Adjustment Expense, Other

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Net Prior Year Claim And Allocated Claim Adjustment Expense Other Professional Liability And Management Liability

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- Definition

Net prior year claim and allocated claim adjustment expense, surety.

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- Definition

Net Prior Year Claim and Allocated Claim Adjustment, General Liability

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Net Prior Year Claim and Allocated Claim Adjustment, Workers Compensation

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- Definition

Pretax favorable unfavorable net prior year claim and allocated claim adjustment expense reserve development excluding life group.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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