Consolidated Statement of Shareholders' Equity (unaudited) - 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 at Dec. 31, 2015					$ 237
Increase (Decrease) in Shareholders' Equity
Net Income	$ 684
Other comprehensive income	121
Ending balance at Sep. 30, 2016					358
Beginning balance at Jun. 30, 2016					383
Increase (Decrease) in Shareholders' Equity
Net Income	479
Other comprehensive income	(25)
Ending balance at Sep. 30, 2016					358
Beginning balance (in shares) at Dec. 31, 2016		127,988,230
Beginning balance at Dec. 31, 2016	6,504	$ 1	$ 1,060	$ 5,289	149	$ 5
Increase (Decrease) in Shareholders' Equity
Net Income	678			678
Dividends ($0.4275 per share)	(53)			(53)
Common stock repurchases (in shares)		(10,734,653)
Common stock repurchases	(431)	$ 0	(431)
Share-based compensation and other (in shares)		683,665
Share-based compensation and other	4	$ 0	8			(4)
Other comprehensive income	177				177
Other	(1)			(1)
Ending balance (in shares) at Sep. 30, 2017		117,937,242
Ending balance at Sep. 30, 2017	6,878	$ 1	637	5,913	326	1
Beginning balance at Jun. 30, 2017					315
Increase (Decrease) in Shareholders' Equity
Net Income	208
Other comprehensive income	11
Ending balance (in shares) at Sep. 30, 2017		117,937,242
Ending balance at Sep. 30, 2017	$ 6,878	$ 1	$ 637	$ 5,913	$ 326	$ 1