Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Treasury Stock
Beginning balance at Dec. 31, 2016	$ 11,279	$ 0	$ 12,294	$ 6,895	$ (7,636)	$ (274)
Beginning 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)	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
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)	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
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 income	4,767			4,767
Dividends declared	(981)			(981)
Other comprehensive income (loss)	(164)				(164)
Shares of common stock issued and compensation expense associated with equity awards (Treasury shares withheld for payment of taxes)	76		114			$ (38)
Shares of common stock issued and compensation expense associated with equity awards (Treasury shares withheld for payment of taxes) (shares)		2				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