Other investments (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Fair Value	$ 14,364	$ 15,683
Finance and Financial Products [Member]
Other Investments [Line Items]
Other investments, Fair Value	2,892	5,719
Available-for-sale Securities [Member]
Other Investments [Line Items]
Other investments, Cost	7,720	12,742
Other investments, Fair Value	17,256	21,402
Available-for-sale Securities [Member] | Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Cost	6,720	9,690
Other investments, Fair Value	14,364	15,683
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	$ 2,892	$ 5,719