Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Change in accounting principle and other	Common Stock	Additional Paid-in Capital	Retained Earnings / (Deficit)	Retained Earnings / (Deficit) Change in accounting principle and other	Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Change in accounting principle and other	Treasury Stock
Beginning balance at Dec. 31, 2017	$ 12,530	$ (260)	$ 0	$ 12,053	$ 8,256	$ (154)	$ (7,621)	$ (106)	$ (158)
Beginning balance (shares) at Dec. 31, 2017			715						7
Consolidated Statements of Stockholders' Equity
Net (loss)/income	3,935				3,935
Dividends declared	(909)				(909)
Other comprehensive loss	(98)						(98)
Common stock issued for employee equity awards and other	51			91					$ (40)
Common stock issued for employee equity awards and other (shares)			1						1	[1]
Stock options exercised	13			13
Stock options exercised (shares)			1
Stock purchased and retired	(1,575)			(486)	(1,089)
Stock purchased and retired (shares)			(29)
Ending balance at Dec. 31, 2018	13,687		$ 0	11,671	10,039		(7,825)		$ (198)
Ending balance (shares) at Dec. 31, 2018			688						8
Consolidated Statements of Stockholders' Equity
Net (loss)/income	4,767				4,767
Dividends declared	(981)				(981)
Other comprehensive loss	(164)						(164)
Common stock issued for employee equity awards and other	76			114					$ (38)
Common stock issued for employee equity awards and other (shares)			2						1	[1]
Stock purchased and retired	(2,027)			(656)	(1,371)
Stock purchased and retired (shares)			(38)
Ending balance at Dec. 31, 2019	15,358		$ 0	11,129	12,454		(7,989)		$ (236)
Ending balance (shares) at Dec. 31, 2019			652						9
Consolidated Statements of Stockholders' Equity
Net (loss)/income	(12,385)				(12,385)
Dividends declared	(257)				(257)
Other comprehensive loss	(1,049)						(1,049)
Common stock issued for employee equity awards and other	97			120					$ (23)
Common stock issued for employee equity awards and other (shares)			1						0	[1]
Stock purchased and retired	(344)			(104)	(240)
Stock purchased and retired (shares)			(6)
Government support warrant issuance	114			114
Ending balance at Dec. 31, 2020	$ 1,534		$ 0	$ 11,259	$ (428)		$ (9,038)		$ (259)
Ending balance (shares) at Dec. 31, 2020			647						9

[1] Treasury shares were withheld for payment of taxes, at a weighted average price per share of $52.17, $50.20 and $54.90 in 2020, 2019 and 2018, respectively.