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Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2011
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |
Catastrophe losses net of reinsurance |  | $ 380 | $ 165 | $ 141 |
Payments for Reinsurance |  | 4 |  |  |
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development Life & Group |  | (79) | (45) | (50) |
Loss Portfolio Transfer |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |
Net A&EP claim and allocated claim adjustment expense reserves ceded to NICO |  |  |  |  | $ 1,600
Aggregate limit under A&EP Loss Portfolio Transfer |  |  |  |  | 4,000
A&EP claim and allocated claim adjustment expense reserves ceded under existing third party reinsurance contracts transferred to NICO under A&EP Loss Portfolio Transfer |  |  |  |  | 1,200
Reinsurance premium paid to NICO under A&EP Loss Portfolio Transfer |  |  |  |  | 2,000
Net reinsurance receivables transferrred to NICO under A&EP Loss Portfolio Transfer |  |  |  |  | 215
Total consideration paid to NICO under AEP Loss Portfolio Transfer |  |  |  |  | $ 2,200
Net A&EP adverse development before consideration of LPT |  | 60 | 200 | $ 150 |
Cumulative amounts ceded under AEP Loss Portfolio Transfer |  | 2,900 | 2,800 |  |
Deferred reinsurance benefit yet to be recognized |  | 326 | 334 |  |
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer |  | 3,100 | $ 2,800 |  |
Hurricane Harvey, Irma and Maria |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |
Catastrophe losses net of reinsurance | $ 188 | $ 256 |  |  |

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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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