Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions		Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning balance at Dec. 31, 2015		$ 10,850	$ 0	$ 12,936	$ 5,562	$ (7,275)	$ (373)
Beginning balance (shares) at Dec. 31, 2015			800				21
Consolidated Statements of Stockholders' Equity
Net income		4,195			4,195
Change in accounting principle		(735)			(735)
Dividends declared		(509)			(509)
Other comprehensive income (loss)		(361)				(361)
Shares of common stock issued and compensation expense associated with equity awards (Treasury shares withheld for payment of taxes)	[1]	65		105			$ (40)
Shares of common stock issued and compensation expense associated with equity awards (Treasury shares withheld for payment of taxes) (shares)	[1]		2				1
Stock options exercised		32		32
Stock options exercised (shares)			3
Treasury stock, net, contributed to our qualified defined benefit pension plans		343		204			$ 139
Treasury stock, net, contributed to our qualified defined benefit pension plans (shares)							(8)
Stock purchased and retired		(2,601)		(983)	(1,618)
Stock purchased and retired (shares)			(60)
Ending balance at Dec. 31, 2016		11,279	$ 0	12,294	6,895	(7,636)	$ (274)
Ending balance (shares) at Dec. 31, 2016			745				14
Consolidated Statements of Stockholders' Equity
Net income		3,205			3,205
Dividends declared		(731)			(731)
Other comprehensive income (loss)		15				15
Shares of common stock issued and compensation expense associated with equity awards (Treasury shares withheld for payment of taxes)	[1]	68		107			$ (39)
Shares of common stock issued and compensation expense associated with equity awards (Treasury shares withheld for payment of taxes) (shares)	[1]		1				1
Stock options exercised		28		28
Stock options exercised (shares)			2
Treasury stock, net, contributed to our qualified defined benefit pension plans		343		188			$ 155
Treasury stock, net, contributed to our qualified defined benefit pension plans (shares)							(8)
Stock purchased and retired		(1,677)		(564)	(1,113)
Stock purchased and retired (shares)			(33)
Ending balance at Dec. 31, 2017		12,530	$ 0	12,053	8,256	(7,621)	$ (158)
Ending balance (shares) at Dec. 31, 2017			715				7
Consolidated Statements of Stockholders' Equity
Net income		3,935			3,935
Change in accounting principle and other		(260)			(154)	(106)
Dividends declared		(909)			(909)
Other comprehensive income (loss)		(98)				(98)
Shares of common stock issued and compensation expense associated with equity awards (Treasury shares withheld for payment of taxes)	[1]	51		91			$ (40)
Shares of common stock issued and compensation expense associated with equity awards (Treasury shares withheld for payment of taxes) (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

[1] Weighted average price per share.