Accumulated other comprehensive income - Reclassified Amounts (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment gains/losses	$ (3,150)	$ (8,266)	$ (5,643)	$ (8,725)
Unrealized appreciation of investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before income taxes			(4,904)	(1,781)
Applicable income taxes			(1,716)	(623)
Total amounts reclassified from other comprehensive income into net earnings			(3,188)	(1,158)
Unrealized appreciation of investments [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment gains/losses			(4,904)	(1,781)
Foreign currency translation [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before income taxes				197
Applicable income taxes				69
Total amounts reclassified from other comprehensive income into net earnings				128
Foreign currency translation [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment gains/losses				197
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			79	2
Applicable income taxes			20	1
Total amounts reclassified from other comprehensive income into net earnings			59	1
Prior service and actuarial gains/losses of defined benefit pension plans [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other			79	2
Other AOCI transactions [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before income taxes			41	18
Applicable income taxes			18	7
Total amounts reclassified from other comprehensive income into net earnings			23	11
Other AOCI transactions [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other			41	18
Accumulated other comprehensive income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications before income taxes			(4,784)	(1,564)
Applicable income taxes			(1,678)	(546)
Total amounts reclassified from other comprehensive income into net earnings			(3,106)	(1,018)
Accumulated other comprehensive income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment gains/losses			(4,904)	(1,584)
Other			$ 120	$ 20