Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated other comprehensive income (loss):
AOCI, beginning balance at Dec. 31, 2017	$ 10,669	$ 6	$ 49	$ 10,544	$ 70
Beginning balance, shares at Dec. 31, 2017		588
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	520			520
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(6)				(7)
Other comprehensive income (loss)	(6)				(6)
Common stock issued, stock-based compensation plans - value	60		60
Common stock issued, stock-based compensation plans - shares		2
Stock-based compensation expense	59		59
Repurchases of common stock, Value	(316)		(105)	(211)
Repurchases of common stock, Shares		(4)
Dividends declared, $0.20 per share	(119)			(119)
AOCI, ending balance at Mar. 31, 2018	10,988	$ 6	63	10,856	63
Ending balance, shares at Mar. 31, 2018		586
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of changes in accounting principle	121			122	(1)
AOCI, beginning balance at Dec. 31, 2018	$ 11,424	$ 6	47	11,485	(114)
Beginning balance, shares at Dec. 31, 2018	577	577
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 441
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	40				40
Other comprehensive income (loss)	40
Common stock issued, stock-based compensation plans - value	50		50
Common stock issued, stock-based compensation plans - shares		2
Stock-based compensation expense	66		66
Repurchases of common stock, Value	(771)		(99)	(672)
Repurchases of common stock, Shares		(10)
Dividends declared, $0.20 per share	(116)			(116)
AOCI, ending balance at Mar. 31, 2019	$ 11,136	$ 6	$ 64	11,140	$ (74)
Ending balance, shares at Mar. 31, 2019	569	569
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of changes in accounting principle	$ 2			$ 2