CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)
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
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 ($0.41 and $0.37 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)
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)
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
Beginning balance at Dec. 31, 2019	12,805	$ (3)	$ 0	$ (5,563)	11,174	7,813	$ (3)	(619)
Balance (in shares) at Dec. 31, 2019			1,197	429
Components of comprehensive income:
Net income	505					505
Other comprehensive income (loss)	(9)							(9)
Issuance of common stock pursuant to employee stock options	27				27
Issuance of common stock pursuant to employee stock options (in shares)			1
Issuance of common stock pursuant to restricted stock units	0
Issuance of common stock pursuant to restricted stock units (in shares)			1
Restricted stock surrendered for employees’ tax liability	(31)				(31)
Share-based compensation expense related to employee stock options and restricted stock units	43				43
Dividends ($0.41 and $0.37 per common share)	(316)					(316)
Ending balance at Mar. 31, 2020	13,021		$ 0	$ (5,563)	11,213	7,999		(628)
Balance (in shares) at Mar. 31, 2020			1,199	429
Beginning balance at Dec. 31, 2019	12,805	$ (3)	$ 0	$ (5,563)	11,174	7,813	$ (3)	(619)
Balance (in shares) at Dec. 31, 2019			1,197	429
Components of comprehensive income:
Net income	1,688
Other comprehensive income (loss)	(14)
Ending balance at Sep. 30, 2020	14,382		$ 0	$ (5,563)	11,395	9,183		(633)
Balance (in shares) at Sep. 30, 2020			1,201	429
Beginning balance at Mar. 31, 2020	13,021		$ 0	$ (5,563)	11,213	7,999		(628)
Balance (in shares) at Mar. 31, 2020			1,199	429
Components of comprehensive income:
Net income	580					580
Other comprehensive income (loss)	(6)							(6)
Issuance of common stock pursuant to employee stock options	44				44
Issuance of common stock pursuant to employee stock options (in shares)			1
Restricted stock surrendered for employees’ tax liability	(3)				(3)
Share-based compensation expense related to employee stock options and restricted stock units	46				46
Ending balance at Jun. 30, 2020	13,682		$ 0	$ (5,563)	11,300	8,579		(634)
Balance (in shares) at Jun. 30, 2020			1,200	429
Components of comprehensive income:
Net income	604					604
Other comprehensive income (loss)	1							1
Issuance of common stock pursuant to employee stock options	43				43
Issuance of common stock pursuant to employee stock options (in shares)			1
Restricted stock surrendered for employees’ tax liability	(6)				(6)
Share-based compensation expense related to employee stock options and restricted stock units	58				58
Ending balance at Sep. 30, 2020	$ 14,382		$ 0	$ (5,563)	$ 11,395	$ 9,183		$ (633)
Balance (in shares) at Sep. 30, 2020			1,201	429