Other investments (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Fair Value	$ 15,415	$ 15,998
Finance and Financial Products [Member]
Other Investments [Line Items]
Other investments, Fair Value	2,078	5,719
Available-for-sale Securities [Member]
Other Investments [Line Items]
Other investments, Cost	10,970	13,022
Other investments, Fair Value	17,493	21,717
Available-for-sale Securities [Member] | Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Cost	9,970	9,970
Other investments, Fair Value	15,415	15,998
Available-for-sale Securities [Member] | Finance and Financial Products [Member]
Other Investments [Line Items]
Other investments, Cost	1,000	3,052
Other investments, Fair Value	$ 2,078	$ 5,719