Income taxes - Deferred taxes (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred tax liabilities:
Investments - unrealized appreciation and cost basis differences	$ 27,669	$ 25,117
Deferred charges reinsurance assumed	2,876	2,798
Property, plant and equipment	39,345	36,770
Goodwill and other intangible assets	11,344	2,770
Other deferred tax liabilities	5,550	4,555
Deferred tax liabilities	86,784	72,010
Deferred tax assets:
Unpaid losses and loss adjustment expenses	(861)	(887)
Unearned premiums	(1,021)	(927)
Accrued liabilities	(3,821)	(3,487)
Other deferred tax assets	(4,122)	(3,510)
Deferred tax assets	(9,825)	(8,811)
Net deferred tax liability	$ 76,959	$ 63,199