Unpaid losses and loss adjustment expenses - Average historical claims duration (Detail) - Insurance Group [Member]
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Dec. 31, 2018 |
| GEICO [Member] |
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| Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
|
| Average annual percentage payout of incurred losses, net of reinsurance, year one |
61.70%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year two |
19.60%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year three |
8.10%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year four |
4.90%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year five |
2.80%
|
| Berkshire Hathaway Reinsurance Group [Member] | Property [Member] |
|
| Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
|
| Average annual percentage payout of incurred losses, net of reinsurance, year one |
19.00%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year two |
36.10%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year three |
18.30%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year four |
7.90%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year five |
4.30%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year six |
3.00%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year seven |
1.50%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year eight |
1.00%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year nine |
0.20%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year ten |
0.10%
|
| Berkshire Hathaway Reinsurance Group [Member] | Casualty [Member] |
|
| Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
|
| Average annual percentage payout of incurred losses, net of reinsurance, year one |
10.40%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year two |
17.80%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year three |
11.50%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year four |
8.50%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year five |
7.40%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year six |
5.10%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year seven |
3.00%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year eight |
1.90%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year nine |
1.80%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year ten |
1.40%
|
| Berkshire Hathaway Primary Group [Member] | Medical Professional Liability [Member] |
|
| Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
|
| Average annual percentage payout of incurred losses, net of reinsurance, year one |
1.60%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year two |
7.30%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year three |
11.50%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year four |
14.50%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year five |
14.10%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year six |
12.40%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year seven |
8.40%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year eight |
6.00%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year nine |
4.10%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year ten |
2.30%
|
| Berkshire Hathaway Primary Group [Member] | Workers' Compensation and Other Casualty [Member] |
|
| Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
|
| Average annual percentage payout of incurred losses, net of reinsurance, year one |
15.80%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year two |
21.50%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year three |
16.50%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year four |
12.00%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year five |
7.60%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year six |
4.60%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year seven |
2.90%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year eight |
1.50%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year nine |
1.00%
|
| Average annual percentage payout of incurred losses, net of reinsurance, year ten |
0.70%
|