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Short Duration Contracts - Percentage annual payout - all segments (Details)	Dec. 31, 2020
Insurance | Property, energy, marine and aviation
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	18.60%
Year Two	41.70%
Year Three	19.60%
Year Four	7.80%
Year Five	3.90%
Year Seven	2.30%
Year Eight	(1.00%)
Year Nine	(0.60%)
Year Ten	0.10%
Year Six	3.30%
Insurance | Third party occurrence business
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	3.20%
Year Two	9.20%
Year Three	11.30%
Year Four	11.60%
Year Five	11.30%
Year Seven	6.20%
Year Eight	3.90%
Year Nine	4.30%
Year Ten	3.60%
Year Six	8.80%
Insurance | Third party claims-made business
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	4.50%
Year Two	18.70%
Year Three	18.40%
Year Four	12.90%
Year Five	12.20%
Year Seven	5.80%
Year Eight	5.20%
Year Nine	3.30%
Year Ten	2.50%
Year Six	7.10%
Insurance | Multi-line and other specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	30.80%
Year Two	27.70%
Year Three	10.50%
Year Four	10.40%
Year Five	6.70%
Year Seven	2.30%
Year Eight	1.20%
Year Nine	1.50%
Year Ten	0.30%
Year Six	4.60%
Reinsurance | Casualty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	2.40%
Year Two	7.20%
Year Three	11.20%
Year Four	12.20%
Year Five	10.30%
Year Seven	7.30%
Year Eight	5.70%
Year Nine	4.80%
Year Ten	3.70%
Year Six	8.40%
Reinsurance | Property catastrophe
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	20.50%
Year Two	30.20%
Year Three	25.10%
Year Four	2.90%
Year Five	(1.20%)
Year Seven	0.70%
Year Eight	1.20%
Year Nine	0.20%
Year Ten	(0.30%)
Year Six	1.40%
Reinsurance | Property catastrophe and property other than property catastrophe
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	26.40%
Year Two	39.50%
Year Three	12.80%
Year Four	5.20%
Year Five	2.30%
Year Seven	2.00%
Year Eight	0.60%
Year Nine	0.30%
Year Ten	(0.60%)
Year Six	0.20%
Reinsurance | Marine and aviation
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	6.50%
Year Two	27.20%
Year Three	19.10%
Year Four	10.00%
Year Five	4.20%
Year Seven	7.90%
Year Eight	(0.20%)
Year Nine	0.20%
Year Ten	0.00%
Year Six	2.20%
Reinsurance | Other specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	26.90%
Year Two	33.90%
Year Three	12.30%
Year Four	5.20%
Year Five	4.30%
Year Seven	2.40%
Year Eight	0.80%
Year Nine	(0.10%)
Year Ten	0.20%
Year Six	3.10%
Mortgage
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	3.00%
Year Two	39.00%
Year Three	27.80%
Year Four	11.10%
Year Five	4.90%
Year Seven	1.10%
Year Eight	0.60%
Year Ten	0.30%
Year Six	2.50%

X

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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.

+ References

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-Publisher FASB
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-Topic 944
-SubTopic 40
-Section 50
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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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