Other investments (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Fair Value	$ 14,418	$ 15,998
Finance and Financial Products [Member]
Other Investments [Line Items]
Other investments, Fair Value	5,392	5,719
Available-for-sale Securities [Member]
Other Investments [Line Items]
Other investments, Cost	13,022	13,022
Other investments, Fair Value	19,810	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	14,418	15,998
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	$ 5,392	$ 5,719