Income taxes - Deferred taxes (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Deferred tax liabilities:
Investments - unrealized appreciation and cost basis differences	$ 25,660	$ 16,075
Deferred charges reinsurance assumed	1,526	1,392
Property, plant and equipment	32,409	29,715
Other deferred tax liabilities	6,278	6,485
Deferred tax liabilities	65,873	53,667
Deferred tax assets:
Unpaid losses and loss adjustment expenses	(817)	(924)
Unearned premiums	(682)	(660)
Accrued liabilities	(3,398)	(3,466)
Derivative contract liabilities	(374)	(1,131)
Other deferred tax assets	(3,160)	(3,603)
Deferred tax assets	(8,431)	(9,784)
Net deferred tax liability	$ 57,442	$ 43,883