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, 2016						$ (629)
Components of comprehensive income:
Net income	$ 858
Other comprehensive income (loss)	(13)
Ending balance at Sep. 30, 2017						(642)
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				1,162
Other comprehensive income (loss)	22					22
Issuance of common stock pursuant to employee stock options	93			93
Issuance of common stock pursuant to employee stock options (in shares)		5
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	(86)			(86)
Restricted stock surrendered for employees' tax liability (in shares)		(1)
Share-based compensation expense related to employee stock options and restricted stock units	174			174
Dividends ($0.34 per common share)	(259)				(259)
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