Other receivables (Detail) - USD ($) $ in Millions |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|---|---|
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||||
| Reinsurance recoverable on unpaid losses | $ 3,060 | $ 3,201 | $ 3,338 | $ 3,307 |
| Insurance and Other [Member] | ||||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||||
| Insurance premiums receivable | 12,452 | 11,058 | ||
| Reinsurance recoverable on unpaid losses | 3,060 | 3,201 | ||
| Trade receivables | 12,617 | 12,031 | ||
| Other | 3,823 | 3,464 | ||
| Allowances for uncollectible accounts | (388) | (362) | ||
| Other receivables | 31,564 | 29,392 | ||
| Railroad, Utilities and Energy [Member] | ||||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||||
| Trade receivables | 3,433 | 3,346 | ||
| Other | 362 | 313 | ||
| Allowances for uncollectible accounts | (129) | (128) | ||
| Receivables | $ 3,666 | $ 3,531 |