CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2017	$ 9,462	$ 0	$ (5,563)	$ 10,747	$ 4,916	$ (638)
Balance (in shares) at Dec. 31, 2017		1,186	429
Components of comprehensive income:
Net income	500				500
Other comprehensive loss	(14)					(14)
Issuance of common stock pursuant to employee stock options	47			47
Issuance of common stock pursuant to employee stock options (in shares)		3
Issuance of common stock pursuant to restricted stock units	0			0
Issuance of common stock pursuant to restricted stock units (in shares)		2
Restricted stock surrendered for employees’ tax liability	(64)			(64)
Restricted stock surrendered for employees' tax liability (in shares)		(1)
Share-based compensation expense related to employee stock options and restricted stock units	56			56
Dividends ($0.37 and $0.34 per common share)	(259)				(259)
Ending balance at Mar. 31, 2018	9,819	$ 0	$ (5,563)	10,786	5,245	(649)
Balance (in shares) at Mar. 31, 2018		1,190	429
Beginning balance at Dec. 31, 2018	11,392	$ 0	$ (5,563)	10,963	6,593	(601)
Balance (in shares) at Dec. 31, 2018		1,192	429
Components of comprehensive income:
Net income	447				447
Other comprehensive loss	(1)					(1)
Issuance of common stock pursuant to employee stock options	30			30
Issuance of common stock pursuant to employee stock options (in shares)		2
Issuance of common stock pursuant to restricted stock units	0			0
Issuance of common stock pursuant to restricted stock units (in shares)		2
Restricted stock surrendered for employees’ tax liability	(45)			(45)
Restricted stock surrendered for employees' tax liability (in shares)		(1)
Share-based compensation expense related to employee stock options and restricted stock units	56			56
Dividends ($0.37 and $0.34 per common share)	(283)				(283)
Ending balance at Mar. 31, 2019	$ 11,596	$ 0	$ (5,563)	$ 11,004	$ 6,757	$ (602)
Balance (in shares) at Mar. 31, 2019		1,195	429