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Additional Information - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Allowance for reinsurance recoverables [Line Items] |  |  |
Total rental expense | $ 70 | $ 69 | $ 67
Operating lease future minimum payments due in next year | 65 |  |
Operating lease future minimum payments due in year two | 57 |  |
Operating lease future minimum payments due in year three | 50 |  |
Operating lease future minimum payments due in year four | 40 |  |
Operating lease future minimum payments due in year five | 35 |  |
Operating lease future minimum payments due after year five | 79 |  |
Commitments to fund limited partnerships | 949 |  |
Retirement and employee savings plan expense | 37 | 45 | 43
Allowance for reinsurance recoverables |  |  |
Allowance for reinsurance recoverables [Line Items] |  |  |
Aggregate allowance for losses on reinsurance recoverables | 18 | 20 |
Net expense reduction against the allowance for losses on reinsurance recoverables | (2) |  |
Reinsurance recoverable write-offs | $ 2 |  |
Maximum | Allowance for reinsurance recoverables |  |  |
Allowance for reinsurance recoverables [Line Items] |  |  |
Net expense reduction against the allowance for losses on reinsurance recoverables |  | $ (1) | $ (1)

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- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41502-112717 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 3) -URI http://asc.fasb.org/extlink&oid=82846649&loc=d3e38371-112697 + Details
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