Other investments (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Fair Value	$ 16,838	$ 14,364
Finance and Financial Products [Member]
Other Investments [Line Items]
Other investments, Fair Value	3,396	2,892
Available-for-sale Securities [Member]
Other Investments [Line Items]
Other investments, Cost	7,720	7,720
Other investments, Fair Value	20,234	17,256
Available-for-sale Securities [Member] | Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Cost	6,720	6,720
Other investments, Fair Value	16,838	14,364
Available-for-sale Securities [Member] | Finance and Financial Products [Member]
Other Investments [Line Items]
Other investments, Cost	1,000	1,000
Other investments, Fair Value	$ 3,396	$ 2,892