Income taxes - Income tax expense reconciliation (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income tax expense reconciliation
Earnings before income taxes	$ 28,105	$ 28,796	$ 22,236
Hypothetical amounts applicable to above computed at the U.S. federal statutory rate	9,837	10,079	7,783
Dividends received deduction and tax exempt interest	(820)	(514)	(518)
State income taxes, less U.S. federal income tax benefit	364	168	250
Foreign tax rate differences	(252)	(256)	(280)
U.S. income tax credits	(333)	(457)	(319)
Non-taxable exchange of investments	(679)
Other differences, net	(182)	(69)	8
Total income taxes	$ 7,935	$ 8,951	$ 6,924