Income taxes - Deferred taxes (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred tax liabilities:
Investments - unrealized appreciation and cost basis differences	$ 24,251	$ 27,669
Deferred charges reinsurance assumed	3,226	2,876
Property, plant and equipment	26,671	39,345
Goodwill and other intangible assets	7,204	11,344
Other deferred tax liabilities	3,216	5,550
Deferred tax liabilities	64,568	86,784
Deferred tax assets:
Unpaid losses and loss adjustment expenses	(1,231)	(1,363)
Unearned premiums	(345)	(1,021)
Accrued liabilities	(2,501)	(3,821)
Other deferred tax assets	(4,309)	(4,122)
Deferred tax assets	(8,386)	(10,327)
Net deferred tax liability	$ 56,182	$ 76,457