Accumulated other comprehensive income (loss) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017		Jan. 01, 2019	Jan. 01, 2018	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss)
Other income (expense)									$ (57)		$ (67)		$ 153
Accumulated other comprehensive income (loss), start of period	$ (1,567)				$ (1,684)				(1,567)		(1,684)
Accumulated other comprehensive income (loss), end of period	(1,567)				(1,684)				(1,567)		(1,684)
Provision (benefit) for income taxes									(1,746)		(1,698)		(3,339)
Reclassifications net of tax	1,098	$ 1,494	$ 1,620	$ 1,881	1,048	$ 1,727	$ 1,707	$ 1,665	6,093	[1]	6,147	[1]	754	[1]
Total
Accumulated Other Comprehensive Income (Loss)
Adjustment to adopt recognition and measurement of financial assets and liabilities guidance																$ (11)
Accumulated other comprehensive income (loss), start of period	(1,567)				(1,684)				(1,567)		(1,684)		(1,192)		$ (1,576)	(1,203)	$ (2,039)
Other comprehensive income (loss), before reclassifications									90		(354)		838
Amounts reclassified from accumulated other comprehensive (income) loss									(81)		(127)		9
Other comprehensive income (loss)									9		(481)		847
Accumulated other comprehensive income (loss), end of period	(1,567)				(1,684)				(1,567)		(1,684)		(1,192)
Foreign currency translation
Accumulated Other Comprehensive Income (Loss)
Adjustment to adopt recognition and measurement of financial assets and liabilities guidance																0
Accumulated other comprehensive income (loss), start of period	(1,487)				(1,601)				(1,487)		(1,601)		(1,205)		(1,503)	(1,205)	(1,970)
Other comprehensive income (loss), before reclassifications									16		(397)		752
Amounts reclassified from accumulated other comprehensive (income) loss									0		1		13
Other comprehensive income (loss)									16		(396)		765
Accumulated other comprehensive income (loss), end of period	(1,487)				(1,601)				(1,487)		(1,601)		(1,205)
Pension and other postretirement benefits
Accumulated Other Comprehensive Income (Loss)
Adjustment to adopt recognition and measurement of financial assets and liabilities guidance																0
Accumulated other comprehensive income (loss), start of period	(3)				12				(3)		12		46		31	46	14
Other comprehensive income (loss), before reclassifications									(4)		(6)		48
Amounts reclassified from accumulated other comprehensive (income) loss									(30)		(28)		(16)
Other comprehensive income (loss)									(34)		(34)		32
Accumulated other comprehensive income (loss), end of period	(3)				12				(3)		12		46
Available-for-sale securities
Accumulated Other Comprehensive Income (Loss)
Adjustment to adopt recognition and measurement of financial assets and liabilities guidance																(11)
Accumulated other comprehensive income (loss), start of period	20				(15)				20		(15)		8		(15)	(3)	32
Other comprehensive income (loss), before reclassifications									35		(12)		41
Amounts reclassified from accumulated other comprehensive (income) loss									0		0		(65)
Other comprehensive income (loss)									35		(12)		(24)
Accumulated other comprehensive income (loss), end of period	20				(15)				20		(15)		8
Derivative financial instruments
Accumulated Other Comprehensive Income (Loss)
Adjustment to adopt recognition and measurement of financial assets and liabilities guidance																0
Accumulated other comprehensive income (loss), start of period	(97)				(80)				(97)		(80)		(41)		(89)	$ (41)	$ (115)
Other comprehensive income (loss), before reclassifications									43		61		(3)
Amounts reclassified from accumulated other comprehensive (income) loss									(51)		(100)		77
Other comprehensive income (loss)									(8)		(39)		74
Accumulated other comprehensive income (loss), end of period	$ (97)				$ (80)				(97)		(80)		(41)
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss)
Reclassifications net of tax									81		127		(9)
Reclassification out of Accumulated Other Comprehensive Income | Foreign currency translation
Accumulated Other Comprehensive Income (Loss)
Other income (expense)									0		(1)		(13)
Provision (benefit) for income taxes									0		0		0
Reclassifications net of tax									0		(1)		(13)
Reclassification out of Accumulated Other Comprehensive Income | Pension and other postretirement benefits
Accumulated Other Comprehensive Income (Loss)
Provision (benefit) for income taxes									(10)		(8)		(9)
Reclassifications net of tax									30		28		16
Reclassification out of Accumulated Other Comprehensive Income | Available-for-sale securities
Accumulated Other Comprehensive Income (Loss)
Other income (expense)									0		0		100
Provision (benefit) for income taxes									0		0		(35)
Reclassifications net of tax									$ 0		$ 0		$ 65
Reclassification of certain tax effects from accumulated other comprehensive income | Total
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets															108
Reclassification of certain tax effects from accumulated other comprehensive income | Foreign currency translation
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets															98
Reclassification of certain tax effects from accumulated other comprehensive income | Pension and other postretirement benefits
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets															19
Reclassification of certain tax effects from accumulated other comprehensive income | Available-for-sale securities
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets															0
Reclassification of certain tax effects from accumulated other comprehensive income | Derivative financial instruments
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets															$ (9)

[1] Profit attributable to common shareholders.