Property and Casualty Unpaid Claims and Claim Expenses - Average Annual Percentage Payout Of Incurred Claims by Age (Details)	Dec. 31, 2017
Homeowners
Year One	78.20%
Year Two	17.10%
Year Three	2.50%
Year Four	1.00%
Year Five	0.90%
Year Six	0.20%
Year Seven	0.10%
Year Eight	0.00%
Year Nine	0.00%
Year Ten	0.00%
Auto liability
Year One	41.00%
Year Two	34.90%
Year Three	13.80%
Year Four	6.30%
Year Five	2.50%
Year Six	1.00%
Year Seven	0.30%
Year Eight	0.10%
Year Nine	0.00%
Year Ten	0.00%
Auto physical damage
Year One	95.40%
Year Two	4.60%
Year Three	0.00%
Year Four	0.00%
Year Five	0.00%
Year Six	0.00%
Year Seven	0.00%
Year Eight	0.00%
Year Nine	0.00%
Year Ten	0.00%

Percentage of average annual payout, after reinsurance, in the eighth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 4G
-URI http://asc.fasb.org/extlink&oid=65670685&loc=SL65671329-158438

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Percentage of average annual payout, after reinsurance, in the fifth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the fourth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the ninth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the first year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the seventh year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the sixth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the tenth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the third year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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Percentage of average annual payout, after reinsurance, in the second year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.

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