Consolidated Statement of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Deferred Equity Compensation [Member]
Beginning balance (in shares) at Dec. 31, 2015		137,928,552
Beginning balance at Dec. 31, 2015	$ 6,063	$ 1	$ 1,342	$ 4,478	$ 237	$ 5
Increase (Decrease) in Shareholders' Equity
Net Income	881			881
Dividends	(70)			(70)
Common stock repurchases (in shares)		(10,721,248)
Common stock repurchases	(306)	$ 0	(306)
Share-based compensation and other (in shares)		780,926
Share-based compensation and other	24	$ 0	24
Other comprehensive income (loss)	(88)				(88)
Ending balance (in shares) at Dec. 31, 2016		127,988,230
Ending balance at Dec. 31, 2016	6,504	$ 1	1,060	5,289	149	5
Increase (Decrease) in Shareholders' Equity
Net Income	730			730
Dividends	(70)			(70)
Common stock repurchases (in shares)		(12,669,643)
Common stock repurchases	(501)	$ 0	(501)
Share-based compensation and other (in shares)		702,265
Share-based compensation and other	10		14			(4)
Other comprehensive income (loss)	167				167
Reclassification of stranded tax effects (see Note 1)				(56)	56
Other	(1)			(1)
Ending balance (in shares) at Dec. 31, 2017		116,020,852
Ending balance at Dec. 31, 2017	6,839	$ 1	573	5,892	372	1
Increase (Decrease) in Shareholders' Equity
Net Income	521			521
Dividends	(71)			(71)
Common stock repurchases (in shares)		(13,243,107)
Common stock repurchases	(500)	$ 0	(500)
Share-based compensation and other (in shares)		894,847
Share-based compensation and other	13	$ 0	13			0
Other comprehensive income (loss)	(247)				(247)
Effect of adoption of ASU 2016-01 (see Note 1)				32	(32)
Ending balance (in shares) at Dec. 31, 2018		103,672,592
Ending balance at Dec. 31, 2018	$ 6,555	$ 1	$ 86	$ 6,374	$ 93	$ 1