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Reserve for Unpaid Losses and Loss Adjustment Expenses - Reconciliation of Loss Development to Liability for Unpaid Losses and Loss Adjustment Expenses, P&C (Details) - USD ($) $ in Millions | 12 Months Ended | 72 Months Ended |
--- | --- | --- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2022 | Dec. 31, 2019
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Unpaid losses and loss adjustment expenses | $ 41,243 | $ 39,659 |  | $ 41,243 |
Asbestos and Environmental |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Unpaid for Accident Years not Displayed in Triangles | 390 |  |  | 390 |
Policyholder Benefits and Claims Incurred, Ceded |  |  | $ 220 | 1,244 |
Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Policyholder Benefits and Claims Incurred, Ceded | 300 |  |  |  |
Deferred Revenue | 209 |  |  | 209 |
Reinsurance Policy, Type [Axis]: Asbestos and Environmental |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Policyholder Benefits and Claims Incurred, Ceded |  |  | 220 |  |
Reinsurance Policy, Type [Axis]: Asbestos and Environmental | Asbestos and Environmental |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Policyholder Benefits and Claims Incurred, Ceded | 1,244 |  |  |  |
Deferred Revenue | 594 |  |  | 594 |
Segment Reconciling Items | Asbestos and Environmental |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Unpaid for Accident Years not Displayed in Triangles | 495 |  |  | 495 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 0 |  |  | 0 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 495 |  |  | 495 |
Reinsurance and Other Recoverables | 1,789 |  |  | 1,789 |
Unpaid losses and loss adjustment expenses | 2,284 |  |  | 2,284 |
Workers’ compensation | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 17,911 |  |  | 17,911 |
Cumulative Paid for Accident Years Displayed in Triangles | (9,516) |  |  | (9,516) |
Unpaid for Accident Years not Displayed in Triangles | 3,295 |  |  | 3,295 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 372 |  |  | 372 |
Amount of discount | 333 |  |  | 333 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 11,729 |  |  | 11,729 |
Reinsurance and Other Recoverables | 1,648 |  |  | 1,648 |
Unpaid losses and loss adjustment expenses | 13,377 |  |  | 13,377 |
General liability | Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Policyholder Benefits and Claims Incurred, Ceded | 105 |  |  |  |
General liability | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 7,509 |  |  | 7,509 |
Cumulative Paid for Accident Years Displayed in Triangles | (3,486) |  |  | (3,486) |
Unpaid for Accident Years not Displayed in Triangles | 1,238 |  |  | 1,238 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 153 |  |  | 153 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 5,414 |  |  | 5,414 |
Reinsurance and Other Recoverables | 1,070 |  |  | 1,070 |
Unpaid losses and loss adjustment expenses | 6,484 |  |  | 6,484 |
Marine [Member] | Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Policyholder Benefits and Claims Incurred, Ceded | 38 |  |  |  |
Marine [Member] | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 1,476 |  |  | 1,476 |
Cumulative Paid for Accident Years Displayed in Triangles | (1,192) |  |  | (1,192) |
Unpaid for Accident Years not Displayed in Triangles | 14 |  |  | 14 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 14 |  |  | 14 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 312 |  |  | 312 |
Reinsurance and Other Recoverables | 266 |  |  | 266 |
Unpaid losses and loss adjustment expenses | 578 |  |  | 578 |
Package business | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 7,218 |  |  | 7,218 |
Cumulative Paid for Accident Years Displayed in Triangles | (5,288) |  |  | (5,288) |
Unpaid for Accident Years not Displayed in Triangles | 87 |  |  | 87 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 112 |  |  | 112 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 2,129 |  |  | 2,129 |
Reinsurance and Other Recoverables | 72 |  |  | 72 |
Unpaid losses and loss adjustment expenses | 2,201 |  |  | 2,201 |
Property | P&C Commercial Lines | Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Policyholder Benefits and Claims Incurred, Ceded | 3 |  |  |  |
Property | P&C Commercial Lines | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 3,922 |  |  | 3,922 |
Cumulative Paid for Accident Years Displayed in Triangles | (3,383) |  |  | (3,383) |
Unpaid for Accident Years not Displayed in Triangles | 26 |  |  | 26 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 20 |  |  | 20 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 585 |  |  | 585 |
Reinsurance and Other Recoverables | 329 |  |  | 329 |
Unpaid losses and loss adjustment expenses | 914 |  |  | 914 |
Automobile liability | P&C Commercial Lines | Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Policyholder Benefits and Claims Incurred, Ceded | 14 |  |  |  |
Automobile liability | P&C Commercial Lines | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 4,025 |  |  | 4,025 |
Cumulative Paid for Accident Years Displayed in Triangles | (2,824) |  |  | (2,824) |
Unpaid for Accident Years not Displayed in Triangles | 22 |  |  | 22 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 26 |  |  | 26 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 1,249 |  |  | 1,249 |
Reinsurance and Other Recoverables | 88 |  |  | 88 |
Unpaid losses and loss adjustment expenses | 1,337 |  |  | 1,337 |
Automobile liability | P&C Personal Lines | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 10,887 |  |  | 10,887 |
Cumulative Paid for Accident Years Displayed in Triangles | (9,584) |  |  | (9,584) |
Unpaid for Accident Years not Displayed in Triangles | 31 |  |  | 31 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 60 |  |  | 60 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 1,394 |  |  | 1,394 |
Reinsurance and Other Recoverables | 23 |  |  | 23 |
Unpaid losses and loss adjustment expenses | 1,417 |  |  | 1,417 |
Commercial automobile physical damage | P&C Commercial Lines | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 181 |  |  | 181 |
Cumulative Paid for Accident Years Displayed in Triangles | (169) |  |  | (169) |
Unpaid for Accident Years not Displayed in Triangles | 4 |  |  | 4 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 1 |  |  | 1 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 17 |  |  | 17 |
Reinsurance and Other Recoverables | (1) |  |  | (1) |
Unpaid losses and loss adjustment expenses | 16 |  |  | 16 |
Professional liability | Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Policyholder Benefits and Claims Incurred, Ceded | 95 |  |  |  |
Professional liability | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 2,609 |  |  | 2,609 |
Cumulative Paid for Accident Years Displayed in Triangles | (1,403) |  |  | (1,403) |
Unpaid for Accident Years not Displayed in Triangles | 67 |  |  | 67 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 43 |  |  | 43 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 1,316 |  |  | 1,316 |
Reinsurance and Other Recoverables | 734 |  |  | 734 |
Unpaid losses and loss adjustment expenses | 2,050 |  |  | 2,050 |
Bond | Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Policyholder Benefits and Claims Incurred, Ceded | 1 |  |  |  |
Bond | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 635 |  |  | 635 |
Cumulative Paid for Accident Years Displayed in Triangles | (260) |  |  | (260) |
Unpaid for Accident Years not Displayed in Triangles | 43 |  |  | 43 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 34 |  |  | 34 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 452 |  |  | 452 |
Reinsurance and Other Recoverables | 15 |  |  | 15 |
Unpaid losses and loss adjustment expenses | 467 |  |  | 467 |
Assumed Reinsurance [Member] | Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Policyholder Benefits and Claims Incurred, Ceded | 27 |  |  |  |
Assumed Reinsurance [Member] | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 1,541 |  |  | 1,541 |
Cumulative Paid for Accident Years Displayed in Triangles | (1,133) |  |  | (1,133) |
Unpaid for Accident Years not Displayed in Triangles | 2 |  |  | 2 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 4 |  |  | 4 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 414 |  |  | 414 |
Reinsurance and Other Recoverables | 50 |  |  | 50 |
Unpaid losses and loss adjustment expenses | 464 |  |  | 464 |
Personal automobile physical damage | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 1,288 |  |  | 1,288 |
Cumulative Paid for Accident Years Displayed in Triangles | (1,250) |  |  | (1,250) |
Unpaid for Accident Years not Displayed in Triangles | 6 |  |  | 6 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 4 |  |  | 4 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 48 |  |  | 48 |
Reinsurance and Other Recoverables | 0 |  |  | 0 |
Unpaid losses and loss adjustment expenses | 48 |  |  | 48 |
Homeowners | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 6,063 |  |  | 6,063 |
Cumulative Paid for Accident Years Displayed in Triangles | (5,728) |  |  | (5,728) |
Unpaid for Accident Years not Displayed in Triangles | 3 |  |  | 3 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 36 |  |  | 36 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 374 |  |  | 374 |
Reinsurance and Other Recoverables | 8 |  |  | 8 |
Unpaid losses and loss adjustment expenses | 382 |  |  | 382 |
Homeowners | P&C Personal Lines | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Paid for Accident Years Displayed in Triangles | (5,728) |  |  | (5,728) |
Other ongoing business | Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Policyholder Benefits and Claims Incurred, Ceded | 17 |  |  |  |
Other ongoing business | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Unpaid for Accident Years not Displayed in Triangles | 178 |  |  | 178 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 6 |  |  | 6 |
Amount of discount | 14 |  |  | 14 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 170 |  |  | 170 |
Reinsurance and Other Recoverables | 333 |  |  | 333 |
Unpaid losses and loss adjustment expenses | 503 |  |  | 503 |
Other operations | Segment Reconciling Items |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Unpaid for Accident Years not Displayed in Triangles | 362 |  |  | 362 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 158 |  |  | 158 |
Amount of discount | 0 |  |  | 0 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 520 |  |  | 520 |
Reinsurance and Other Recoverables | 41 |  |  | 41 |
Unpaid losses and loss adjustment expenses | 561 |  |  | 561 |
Property and Casualty Insurance Products |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Cumulative Incurred for Accident Years Displayed in Triangles | 65,265 |  |  | 65,265 |
Cumulative Paid for Accident Years Displayed in Triangles | (45,216) |  |  | (45,216) |
Unpaid for Accident Years not Displayed in Triangles | 5,873 |  |  | 5,873 |
Unpaid Unallocated Loss Adjustment Expenses, Net of Reinsurance | 1,043 |  |  | 1,043 |
Amount of discount | 347 | 355 | 367 | 347 |
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance | 26,618 | 25,368 | 23,897 | 26,618 | $ 22,986
Reinsurance and Other Recoverables | 6,465 | 6,081 | 5,725 | 6,465 | 5,275
Unpaid losses and loss adjustment expenses | 33,083 | 31,449 | 29,622 | $ 33,083 | $ 28,261
Policyholder Benefits and Claims Incurred, Ceded | $ 1,338 | $ 1,243 | $ 1,156 |  |

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- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
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- Definition Liability as of the balance sheet date for amounts representing estimated cost of settling unpaid claims under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims. This includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(13)(a)) -URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
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- Definition Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to the ceding insurer but not yet paid and amounts expected for incurred losses and settlement expenses, which have not yet been reported to the ceding insurer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 6 -URI https://asc.fasb.org/extlink&oid=99404803&loc=d3e21412-158489 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 5 -URI https://asc.fasb.org/extlink&oid=99397103&loc=d3e6824-158387 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
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- Definition Undiscounted amount, after reinsurance, of incurred claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4B -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=116884468&loc=SL65671311-158438 + Details
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- Definition Undiscounted amount, after reinsurance, of the liability for unpaid claims and allocated claim adjustment expense for short-duration insurance contracts for accident years not separately presented in claim development information. Excludes unallocated claim adjustment expense. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4B -URI https://asc.fasb.org/extlink&oid=116884468&loc=SL65671311-158438 + Details
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