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Claim and Claim Adjustment Expense Reserves - Additional Information (Detail) - CNA Financial [Member] - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016 | Dec. 31, 2010 | Dec. 31, 2016
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |
Catastrophe losses, net of reinsurance | $ 269 | $ 16 | $ 342 | $ 137 |  |
Catastrophe-related reinsurance reinstatement premium | 6 |  | 6 |  |  |
Net A&EP adverse development before consideration of LPT |  |  | 60 | $ 200 |  |
Fair value of the collateral trust account | 2,900 |  | 2,900 |  |  | $ 2,800
Hurricane Harvey [Member] |  |  |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |
Catastrophe losses, net of reinsurance | 149 |  | 149 |  |  |
Hurricane Irma [Member] |  |  |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |
Catastrophe losses, net of reinsurance | 95 |  | 95 |  |  |
Hurricane Maria [Member] |  |  |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |
Catastrophe losses, net of reinsurance | 20 |  | 20 |  |  |
Asbestos and Environmental Pollution Reserves [Member] |  |  |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |
Net A&EP claim and allocated claim adjustment expense reserves |  |  |  |  | $ 1,600 |
Aggregate limit under A&EP Loss Portfolio Transfer |  |  |  |  | 4,000 |
Ceded A&EP claim and allocated claim adjustment expense reserves |  |  |  |  | 1,200 |
Reinsurance premium paid to NICO under A&EP Loss Portfolio Transfer |  |  |  |  | 2,000 |
Net reinsurance receivables transferred to NICO under A&EP Loss Portfolio Transfer |  |  |  |  | 215 |
Total consideration |  |  |  |  | $ 2,200 |
Cumulative amounts ceded under the Loss Portfolio Transfer | 2,900 |  | 2,900 |  |  | 2,800
Remaining unrecognized retroactive reinsurance benefit | $ 334 |  | $ 334 |  |  | $ 334

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- Definition Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to asbestos and environmental claims, net of estimated reinsurance recoveries. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 + Details
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