Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Preferred Stock	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2018	$ 12,128	$ 0	$ 937	$ (3,816)	$ 7,238	$ 7,706	$ 63
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax	(31)					(31)
Shares issued - stock-based compensation	62			101	(39)
Shares repurchased	(30)			(30)
Stock-based compensation	(50)				(50)
Net income	174					174
Other comprehensive income (loss)	(4)						(4)
Dividends paid (per share amount of $0.05)	(41)					(41)
Ending balance at Mar. 31, 2019	12,208	0	937	(3,745)	7,149	7,808	59
Beginning balance at Dec. 31, 2019	12,153	0	937	(4,089)	7,207	7,993	105
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax	(12)					(12)
Shares issued - stock-based compensation	38			121	(83)
Shares repurchased	(91)			(91)
Stock-based compensation	(22)				(22)
Net income	(46)					(46)
Other comprehensive income (loss)	(22)						(22)
Dividends paid (per share amount of $0.05)	(40)					(40)
Ending balance at Mar. 31, 2020	$ 11,958	$ 0	$ 937	$ (4,059)	$ 7,102	$ 7,895	$ 83