Other investments (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Fair Value	$ 15,011	$ 16,346
Finance and Financial Products [Member]
Other Investments [Line Items]
Other investments, Fair Value	5,565	5,978
Available-for-sale Securities [Member]
Other Investments [Line Items]
Other investments, Cost	13,022	13,022
Other investments, Fair Value	20,576	22,324
Available-for-sale Securities [Member] | Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Cost	9,970	9,970
Other investments, Fair Value	15,011	16,346
Available-for-sale Securities [Member] | Finance and Financial Products [Member]
Other Investments [Line Items]
Other investments, Cost	3,052	3,052
Other investments, Fair Value	$ 5,565	$ 5,978