Retroactive reinsurance contracts - Narrative (Detail) - USD ($)
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3 Months Ended |
12 Months Ended |
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Feb. 02, 2017 |
Dec. 31, 2017 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
| Effects of Reinsurance [Line Items] |
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| Unpaid losses and loss adjustment expenses under retroactive reinsurance contracts |
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$ 42,937,000,000
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$ 41,834,000,000
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$ 42,937,000,000
|
$ 24,972,000,000
|
$ 24,058,000,000
|
| Deferred charges under retroactive reinsurance contracts |
|
15,278,000,000
|
14,104,000,000
|
15,278,000,000
|
8,047,000,000
|
$ 7,687,000,000
|
| Retroactive Reinsurance [Member] |
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| Effects of Reinsurance [Line Items] |
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| Incurred losses and loss adjustment expenses |
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1,436,000,000
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11,733,000,000
|
1,713,000,000
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| Incurred losses and loss adjustment expenses, prior years' contracts |
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|
919,000,000
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458,000,000
|
451,000,000
|
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| Liabilities for environmental, asbestos and latent injury claims |
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14,000,000,000
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13,100,000,000
|
14,000,000,000
|
|
|
| Unpaid Losses and Loss Adjustment Expenses [Member] | Retroactive Reinsurance [Member] |
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|
|
|
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| Effects of Reinsurance [Line Items] |
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| Incurred losses and loss adjustment expenses |
|
|
262,000,000
|
18,964,000,000
|
2,073,000,000
|
|
| Incurred losses and loss adjustment expenses, prior years' contracts |
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|
(341,000,000)
|
(41,000,000)
|
(63,000,000)
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| Deferred Charges Reinsurance Assumed [Member] | Retroactive Reinsurance [Member] |
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| Effects of Reinsurance [Line Items] |
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| Incurred losses and loss adjustment expenses |
|
|
1,174,000,000
|
(7,231,000,000)
|
(360,000,000)
|
|
| Incurred losses and loss adjustment expenses, prior years' contracts |
|
|
1,260,000,000
|
499,000,000
|
$ 514,000,000
|
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| NICO [Member] | AIG [Member] | Retroactive Reinsurance [Member] |
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| Effects of Reinsurance [Line Items] |
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| Percentage of losses and allocated loss adjustment expenses reinsured in excess of retained amount |
80.00%
|
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| Losses and allocated loss adjustment expenses retained amount |
$ 25,000,000,000
|
|
|
|
|
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| Premiums earned |
10,200,000,000
|
|
|
|
|
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| Unpaid losses and loss adjustment expenses under retroactive reinsurance contracts |
16,400,000,000
|
18,200,000,000
|
18,200,000,000
|
18,200,000,000
|
|
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| Deferred charges under retroactive reinsurance contracts |
6,200,000,000
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7,500,000,000
|
$ 6,900,000,000
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$ 7,500,000,000
|
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| NICO [Member] | AIG [Member] | Retroactive Reinsurance [Member] | Maximum [Member] |
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| Effects of Reinsurance [Line Items] |
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| Losses and allocated loss adjustment expenses reinsured in excess of retained amount |
$ 25,000,000,000
|
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| NICO [Member] | Unpaid Losses and Loss Adjustment Expenses [Member] | AIG [Member] | Retroactive Reinsurance [Member] |
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| Effects of Reinsurance [Line Items] |
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| Incurred losses and loss adjustment expenses |
|
1,800,000,000
|
|
|
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| NICO [Member] | Deferred Charges Reinsurance Assumed [Member] | AIG [Member] | Retroactive Reinsurance [Member] |
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| Effects of Reinsurance [Line Items] |
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| Incurred losses and loss adjustment expenses |
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$ (1,700,000,000)
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