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, 2014		158,306,661
Beginning balance at Dec. 31, 2014	$ 5,758	$ 2	$ 1,887	$ 3,494	$ 370	$ 5
Increase (Decrease) in Shareholders' Equity
Net Income	1,056			1,056
Dividends (2015 $0.48, 2016 $0.52, 2017 $0.57 per share)	(72)			(72)
Common stock repurchases (in shares)		(20,995,419)
Common stock repurchases	(555)	$ (1)	(554)
Share-based compensation and other (in shares)		617,310
Share-based compensation and other	9	$ 0	9
Other comprehensive loss	(133)				(133)
Ending balance (in shares) at Dec. 31, 2015		137,928,552
Ending balance at Dec. 31, 2015	6,063	$ 1	1,342	4,478	237	5
Increase (Decrease) in Shareholders' Equity
Net Income	881			881
Dividends (2015 $0.48, 2016 $0.52, 2017 $0.57 per share)	(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		24
Other comprehensive 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 (2015 $0.48, 2016 $0.52, 2017 $0.57 per share)	(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	$ 0	14			(4)
Other comprehensive loss	167				167
Reclassification of stranded tax effects	0			(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