Condensed 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, 2016					$ 149
Increase (Decrease) in Shareholders' Equity
Net Income	$ 678
Other comprehensive loss	177
Ending balance at Sep. 30, 2017					326
Beginning balance at Jun. 30, 2017					315
Increase (Decrease) in Shareholders' Equity
Net Income	208
Other comprehensive loss	11
Ending balance at Sep. 30, 2017					326
Increase (Decrease) in Shareholders' Equity
Effect of adoption of ASU	(32)
Effect of adoption of ASU | Accounting Standards Update 2016-01 [Member]				$ 32	(32)
Beginning balance (in shares) at Dec. 31, 2017		116,020,852
Beginning balance at Dec. 31, 2017	6,839	$ 1	$ 573	5,892	372	$ 1
Increase (Decrease) in Shareholders' Equity
Net Income	433			433
Dividends ($0.48 per share)	(54)			(54)
Common stock repurchases (in shares)		(10,250,175)
Common stock repurchases	(380)	$ 0	(380)
Share-based compensation and other (in shares)		867,024
Share-based compensation and other	7	$ 0	7
Other comprehensive loss	(262)				(262)
Ending balance (in shares) at Sep. 30, 2018		106,637,701
Ending balance at Sep. 30, 2018	6,583	$ 1	200	6,303	78	1
Beginning balance at Jun. 30, 2018					152
Increase (Decrease) in Shareholders' Equity
Net Income	161
Other comprehensive loss	(74)
Ending balance (in shares) at Sep. 30, 2018		106,637,701
Ending balance at Sep. 30, 2018	$ 6,583	$ 1	$ 200	$ 6,303	$ 78	$ 1