Income taxes - Deferred taxes (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred tax liabilities:
Investments – unrealized appreciation and cost basis differences	$ 40,181	$ 32,134
Deferred charges reinsurance assumed	2,613	2,890
Property, plant and equipment and equipment held for lease	30,203	29,388
Goodwill and other intangible assets	6,753	7,293
Other	3,736	3,144
Deferred tax liabilities	83,486	74,849
Deferred tax assets:
Unpaid losses and loss adjustment expenses	(1,135)	(1,086)
Unearned premiums	(900)	(853)
Accrued liabilities	(2,193)	(1,981)
Regulatory liabilities	(1,421)	(1,610)
Other	(4,576)	(3,496)
Deferred tax assets	(10,225)	(9,026)
Net deferred tax liability	$ 73,261	$ 65,823