Shareholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Additional Paid-in Capital	$ 3,002	$ 3,002		$ 3,806
Common Stock and Additional Paid-in Capital Percentage Change	21.00%	21.00%
Common Stock and Additional Paid-in Capital Change	$ 804	$ 804
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ 49	$ 49	$ (361)	$ (250)	$ (139)
Stock Repurchased During Period, Shares	6,600,000	18,000,000.0	7,800,000
Shares, Issued	170,400,000	170,400,000
Treasury Stock Acquired, Average Cost Per Share	$ 41.43	$ 45.89	$ 53.84
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 275	$ 275
Common Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001
Stock Repurchased and Retired During Period, Value	$ 275	$ 825	$ 420
Common Stock, Terms of Conversion	1.07
Warrant [Member]
Warrant Exercise Price	$ 34.14	$ 34.14
Class of Warrant or Right, Outstanding	29,300,000	29,300,000