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Reinsurance - California E&S Earthquake Contract (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($) contract | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Ceded Credit Risk [Line Items] |  |  |
Ceded premium earned | $ 1,274 | $ 1,296 | $ 1,338
E&S Earthquake Agreement |  |  |
Ceded Credit Risk [Line Items] |  |  |
Contracts number | contract | 1 |  |
Catastrophe insurance, quota share basis, percentage | 100.00% |  |
Ceded premium earned | $ 344 | $ 381 | $ 414

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- Definition Amount of earned premiums ceded to other entities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.1) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (b),(c)(2) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=84167274&loc=d3e27175-158546 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 2 -Subparagraph (SX 210.12-17) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915 + Details
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- Details
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