Accumulated other comprehensive income - Reclassified Amounts (Detail) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Unrealized appreciation of investments, net [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before income taxes	$ (265)	$ (589)
Applicable income taxes	(56)	(206)
Total reclassifications into net earnings	(209)	(383)
Prior service and actuarial gains/losses of defined benefit pension plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before income taxes	84	45
Applicable income taxes	22	11
Total reclassifications into net earnings	62	34
Other AOCI transactions [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before income taxes	(8)	24
Applicable income taxes	(3)	11
Total reclassifications into net earnings	(5)	13
Accumulated other comprehensive income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before income taxes	(189)	(520)
Applicable income taxes	(37)	(184)
Total reclassifications into net earnings	$ (152)	$ (336)

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount before tax of reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss).

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