Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Open Market Repurchases [Member]	Common Stock [Member]	Treasury Stock [Member]	Treasury Stock [Member] Open Market Repurchases [Member]	Common Stock Shares Outstanding [Member]	Common Stock Shares Outstanding [Member] Open Market Repurchases [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Total Stockholders' Equity [Member]	Total Stockholders' Equity [Member] Open Market Repurchases [Member]	Noncontrolling Interest [Member]
Beginning Balance, Value at Dec. 31, 2017	$ 3,485		$ 4	$ (2,692)				$ 3,077	$ 61	$ 3,004	$ 3,454		$ 31
Beginning Balance, Shares at Dec. 31, 2017			439,718,145	(176,667,573)		263,050,572
Comprehensive income:
Net income	210									210	210
Other comprehensive income (loss), net of tax	129								129		129
Total comprehensive income	339										339
Cash dividends:
Common stock	(85)									(85)	(85)
Dividend equivalent units related to employee stock-based compensation plans	(2)									(2)	(2)
Issuance of common shares	$ 39							39			39
Issuance of common shares, Shares	5,134,238		5,134,238			5,134,238
Stock-based compensation expense	$ 18							18			18
Common stock repurchased, Shares						0
Shares repurchased related to employee stock-based compensation plans	$ (49)			$ (49)							(49)
Shares repurchased related to employee stock-based compensation plans, Shares	(3,557,504)			(3,557,504)		(3,557,504)
Reclassification from adoption of ASU No. 2018-02									13	(13)
Ending Balance, Value at Jun. 30, 2018	$ 3,745		$ 4	$ (2,741)				3,134	203	3,114	3,714		31
Ending Balance, Shares at Jun. 30, 2018			444,852,383	(180,225,077)		264,627,306
Beginning Balance, Value at Mar. 31, 2018	3,668		$ 4	$ (2,740)				3,127	173	3,073	3,637		31
Beginning Balance, Shares at Mar. 31, 2018			444,739,212	(180,132,708)		264,606,504
Comprehensive income:
Net income	83									83	83
Other comprehensive income (loss), net of tax	30								30		30
Total comprehensive income	113										113
Cash dividends:
Common stock	(42)									(42)	(42)
Issuance of common shares	$ 1							1			1
Issuance of common shares, Shares	113,171		113,171			113,171
Stock-based compensation expense	$ 6							6			6
Shares repurchased related to employee stock-based compensation plans	$ (1)			$ (1)							(1)
Shares repurchased related to employee stock-based compensation plans, Shares	(92,369)			(92,369)		(92,369)
Ending Balance, Value at Jun. 30, 2018	$ 3,745		$ 4	$ (2,741)				3,134	203	3,114	3,714		31
Ending Balance, Shares at Jun. 30, 2018			444,852,383	(180,225,077)		264,627,306
Beginning Balance, Value at Dec. 31, 2018	3,547		$ 4	$ (2,961)				3,145	113	3,218	3,519		28
Beginning Balance, Shares at Dec. 31, 2018			445,377,826	(197,940,553)		247,437,273
Comprehensive income:
Net income	281									281	281
Other comprehensive income (loss), net of tax	(193)								(193)		(193)
Total comprehensive income	88										88
Cash dividends:
Common stock	(76)									(76)	(76)
Dividend equivalent units related to employee stock-based compensation plans	(5)									(5)	(5)
Issuance of common shares	$ 19							19			19
Issuance of common shares, Shares	4,625,347		4,625,347			4,625,347
Stock-based compensation expense	$ 17							17			17
Common stock repurchased		$ (233)			$ (233)	$ (233)						$ (233)
Common stock repurchased, Shares					(19,034,252)	(19,034,252)	(19,034,252)
Shares repurchased related to employee stock-based compensation plans	$ (28)			$ (28)							(28)
Shares repurchased related to employee stock-based compensation plans, Shares	(2,534,090)			(2,534,090)		(2,534,090)
Net activity in noncontrolling interest	$ (17)												(17)
Ending Balance, Value at Jun. 30, 2019	3,312		$ 4	$ (3,222)				3,181	(80)	3,418	3,301		11
Ending Balance, Shares at Jun. 30, 2019			450,003,173	(219,508,895)		230,494,278
Beginning Balance, Value at Mar. 31, 2019	3,443		$ 4	$ (3,094)				3,174	43	3,303	3,430		13
Beginning Balance, Shares at Mar. 31, 2019			449,807,290	(209,771,402)		240,035,888
Comprehensive income:
Net income	153									153	153
Other comprehensive income (loss), net of tax	(123)								(123)		(123)
Total comprehensive income	30										30
Cash dividends:
Common stock	(37)									(37)	(37)
Dividend equivalent units related to employee stock-based compensation plans	(1)									(1)	(1)
Issuance of common shares	$ 2							2			2
Issuance of common shares, Shares	195,883		195,883			195,883
Stock-based compensation expense	$ 5							5			5
Common stock repurchased		$ (126)			$ (126)	$ (126)						$ (126)
Common stock repurchased, Shares					(9,617,008)	(9,617,008)	(9,617,008)
Shares repurchased related to employee stock-based compensation plans	$ (2)			$ (2)							(2)
Shares repurchased related to employee stock-based compensation plans, Shares	(120,485)			(120,485)		(120,485)
Net activity in noncontrolling interest	$ (2)												(2)
Ending Balance, Value at Jun. 30, 2019	$ 3,312		$ 4	$ (3,222)				$ 3,181	$ (80)	$ 3,418	$ 3,301		$ 11
Ending Balance, Shares at Jun. 30, 2019			450,003,173	(219,508,895)		230,494,278