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 income (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, 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	1,162
Other comprehensive income (loss)	22
Ending balance at Sep. 30, 2018	10,659	$ 0	$ (5,563)	10,928	5,907	(613)
Balance (in shares) at Sep. 30, 2018		1,192	429
Beginning 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
Components of comprehensive income:
Net income	402				402
Other comprehensive income (loss)	44					44
Issuance of common stock pursuant to employee stock options	30			30
Issuance of common stock pursuant to employee stock options (in shares)		1
Restricted stock surrendered for employees’ tax liability	(10)			(10)
Restricted stock surrendered for employees' tax liability (in shares)		0
Share-based compensation expense related to employee stock options and restricted stock units	61			61
Ending balance at Jun. 30, 2018	10,346	$ 0	$ (5,563)	10,867	5,647	(605)
Balance (in shares) at Jun. 30, 2018		1,191	429
Components of comprehensive income:
Net income	260				260
Other comprehensive income (loss)	(8)					(8)
Issuance of common stock pursuant to employee stock options	16			16
Issuance of common stock pursuant to employee stock options (in shares)		1
Restricted stock surrendered for employees’ tax liability	(12)			(12)
Restricted stock surrendered for employees' tax liability (in shares)		0
Share-based compensation expense related to employee stock options and restricted stock units	57			57
Ending balance at Sep. 30, 2018	10,659	$ 0	$ (5,563)	10,928	5,907	(613)
Balance (in shares) at Sep. 30, 2018		1,192	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 income (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
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	978
Other comprehensive income (loss)	(6)
Ending balance at Sep. 30, 2019	12,235	$ 0	$ (5,563)	11,116	7,289	(607)
Balance (in shares) at Sep. 30, 2019		1,197	429
Beginning 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
Components of comprehensive income:
Net income	328				328
Other comprehensive income (loss)	(6)					(6)
Issuance of common stock pursuant to employee stock options	28			28
Issuance of common stock pursuant to employee stock options (in shares)		1
Restricted stock surrendered for employees’ tax liability	(4)			(4)
Restricted stock surrendered for employees' tax liability (in shares)		0
Share-based compensation expense related to employee stock options and restricted stock units	35			35
Ending balance at Jun. 30, 2019	11,977	$ 0	$ (5,563)	11,063	7,085	(608)
Balance (in shares) at Jun. 30, 2019		1,196	429
Components of comprehensive income:
Net income	204				204
Other comprehensive income (loss)	1					1
Issuance of common stock pursuant to employee stock options	29			29
Issuance of common stock pursuant to employee stock options (in shares)		1
Restricted stock surrendered for employees’ tax liability	(8)			(8)
Restricted stock surrendered for employees' tax liability (in shares)		0
Share-based compensation expense related to employee stock options and restricted stock units	32			32
Ending balance at Sep. 30, 2019	$ 12,235	$ 0	$ (5,563)	$ 11,116	$ 7,289	$ (607)
Balance (in shares) at Sep. 30, 2019		1,197	429