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Related party transaction (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ceded Premiums Written |  |  |  |  |  |  |  |  | $ 7,389 | $ 7,132 | $ 6,838
Losses and loss expenses | $ 4,610 | $ 4,868 | $ 4,487 | $ 4,102 | $ 4,272 | $ 6,247 | $ 4,146 | $ 3,789 | 18,067 | 18,454 | 16,052
Reinsurance recoverable on losses and loss expenses | 15,993 |  |  |  | 15,034 |  |  |  | 15,993 | 15,034 |
Insurance and reinsurance balances payable | 6,437 |  |  |  | 5,868 |  |  |  | 6,437 | 5,868 |
Net premiums written |  |  |  |  |  |  |  |  | 30,579 | 29,244 | 28,145
Starr Technical Risk Agency and Affiliates [Member] |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |
Premiums Written, Gross |  |  |  |  |  |  |  |  | 411 | 464 | 658
Ceded Premiums Written |  |  |  |  |  |  |  |  | 188 | 175 | 208
Paid commissions |  |  |  |  |  |  |  |  | 84 | 101 | 145
Commissions received |  |  |  |  |  |  |  |  | 42 | 37 | 56
Losses and loss expenses |  |  |  |  |  |  |  |  | 188 | 438 | 313
Reinsurance recoverable on losses and loss expenses | 514 |  |  |  | 557 |  |  |  | 514 | 557 |
Insurance and reinsurance balances payable | 75 |  |  |  | 44 |  |  |  | 75 | 44 |
Minimum Amount of Program Business to be Written to Earn Profit Sharing |  |  |  |  |  |  |  |  | 20 |  |
ABR Reinsurance Capital Holdings Ltd. [Member] |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ceded Premiums Written |  |  |  |  |  |  |  |  | 329 | 342 | 288
Commissions received |  |  |  |  |  |  |  |  | 96 | 94 | $ 66
Reinsurance recoverable on losses and loss expenses | 557 |  |  |  | 365 |  |  |  | 557 | 365 |
Insurance and reinsurance balances payable | $ 47 |  |  |  | $ 51 |  |  |  | $ 47 | $ 51 |
Equity Method Investment, Ownership Percentage | 11.70% |  |  |  |  |  |  |  | 11.70% |  |
Warrants & Rights Outstanding | 0.50% |  |  |  |  |  |  |  | 0.50% |  |

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- Definition The known and estimated amount recoverable as of the balance sheet date from reinsurers for claims paid or incurred by the ceding insurer and associated claims settlement expenses, including estimated amounts for claims incurred but not reported net of any related valuation allowance. + References No definition available. + Details
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- Definition Amount of written premiums ceded to other entities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
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