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Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2017 | Sep. 30, 2017 | Dec. 31, 2016
Commitments [Line Items] |  |  |
Future policy benefits | $ 11,040 | $ 11,040 | $ 10,326
CNA Financial [Member] |  |  |
Commitments [Line Items] |  |  |
Aggregate amount related to indemnification agreements | 254 | 254 |
Aggregate amount related to quantifiable guarantees | 375 | 375 |
Potential amount of future payments under guarantees | 1,800 | 1,800 |
Increase (decrease) in premium development recognized | 0 | (37) |
Decrease in pretax income | 1 | 7 |
CNA Financial [Member] | Workers Compensation Policy [Member] |  |  |
Commitments [Line Items] |  |  |
Future policy benefits | $ 61 | $ 61 |

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- Definition Commitments [Line Items] + References No definition available. + Details
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- Definition Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248 + Details
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- Definition Amount of accrued obligation to policyholders that relates to insured events for long-duration contracts. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 25 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28366191&loc=d3e13145-158430 Reference 2: 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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.13(a)(1)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 4: 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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