Other investments (Detail) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016
Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Fair Value		$ 3,303	$ 14,364
Available-for-sale Securities [Member]
Other Investments [Line Items]
Other investments, Cost		2,749	7,720
Other investments, Fair Value		3,311	17,256
Available-for-sale Securities [Member] | Insurance and Other [Member]
Other Investments [Line Items]
Other investments, Cost		2,743	6,720
Other investments, Fair Value		3,303	14,364
Available-for-sale Securities [Member] | Finance and Financial Products [Member] | Other Assets [Member]
Other Investments [Line Items]
Other investments, Cost	[1]	6	1,000
Other investments, Fair Value	[1]	$ 8	$ 2,892

[1] Included in other assets.