Other investments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Fair Value	$ 16,346	$ 12,334
Finance and Financial Products [Member]
Other Investments [Line Items]
Other investments, Fair Value	5,978	5,617
Available-for-sale Securities [Member]
Other Investments [Line Items]
Other investments, Cost	13,022	10,022
Other investments, Fair Value	22,324	17,951
Available-for-sale Securities [Member] | Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Cost	9,970	6,970
Other investments, Fair Value	16,346	12,334
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	$ 5,978	$ 5,617