Accumulated other comprehensive income (loss) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss)
Other income (expense)									$ 146		$ 161		$ 322
Accumulated other comprehensive income (loss), start of period				$ (2,035)				$ (1,059)	(2,035)		(1,059)		231
Other comprehensive income (loss), before reclassifications									48		(993)		(1,245)
Amounts reclassified from accumulated other comprehensive (income) loss									(52)		17		(45)
Other comprehensive income (loss)									(4)		(976)		(1,290)
Accumulated other comprehensive income (loss), end of period	$ (2,039)				$ (2,035)				(2,039)		(2,035)		(1,059)
Provision (benefit) for income taxes									192		916		692
Reclassifications net of tax	(1,171)	$ 283	$ 550	271	(94)	$ 559	$ 802	1,245	(67)	[1]	2,512	[1]	2,452	[1]
Foreign currency translation
Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss), start of period				(1,953)				(992)	(1,953)		(992)		163
Other comprehensive income (loss), before reclassifications									(34)		(961)		(1,155)
Amounts reclassified from accumulated other comprehensive (income) loss									17		0		0
Other comprehensive income (loss)									(17)		(961)		(1,155)
Accumulated other comprehensive income (loss), end of period	(1,970)				(1,953)				(1,970)		(1,953)		(992)
Pension and other postretirement benefits
Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss), start of period				(69)				(31)	(69)		(31)		(10)
Other comprehensive income (loss), before reclassifications									118		(3)		4
Amounts reclassified from accumulated other comprehensive (income) loss									(35)		(35)		(25)
Other comprehensive income (loss)									83		(38)		(21)
Accumulated other comprehensive income (loss), end of period	14				(69)				14		(69)		(31)
Derivative financial instruments
Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss), start of period				(50)				(119)	(50)		(119)		(5)
Other comprehensive income (loss), before reclassifications									(62)		(19)		(118)
Amounts reclassified from accumulated other comprehensive (income) loss									(3)		88		4
Other comprehensive income (loss)									(65)		69		(114)
Accumulated other comprehensive income (loss), end of period	(115)				(50)				(115)		(50)		(119)
Available-for-sale securities
Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss), start of period				$ 37				$ 83	37		83		83
Other comprehensive income (loss), before reclassifications									26		(10)		24
Amounts reclassified from accumulated other comprehensive (income) loss									(31)		(36)		(24)
Other comprehensive income (loss)									(5)		(46)		0
Accumulated other comprehensive income (loss), end of period	$ 32				$ 37				32		37		83
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss)
Reclassifications net of tax									52		(17)		45
Reclassification out of Accumulated Other Comprehensive Income | Foreign currency translation
Accumulated Other Comprehensive Income (Loss)
Other income (expense)									(17)		0		0
Provision (benefit) for income taxes									0		0		0
Reclassifications net of tax									(17)		0		0
Reclassification out of Accumulated Other Comprehensive Income | Pension and other postretirement benefits
Accumulated Other Comprehensive Income (Loss)
Provision (benefit) for income taxes									21		18		13
Reclassifications net of tax									35		35		25
Reclassification out of Accumulated Other Comprehensive Income | Derivative financial instruments
Accumulated Other Comprehensive Income (Loss)
Provision (benefit) for income taxes									2		(51)		(2)
Reclassifications net of tax									3		(88)		(4)
Reclassification out of Accumulated Other Comprehensive Income | Available-for-sale securities
Accumulated Other Comprehensive Income (Loss)
Other income (expense)									46		56		35
Provision (benefit) for income taxes									15		20		11
Reclassifications net of tax									$ 31		$ 36		$ 24

[1] 1 Profit (loss) attributable to common stockholders.