Shareholders' Equity (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jul. 17, 2019	Apr. 26, 2018	Dec. 31, 2016
Treasury Stock, Value, Acquired	$ 151	$ 244	$ 674	$ 814
The 2016 Repurchase Program [Member]
Stock Repurchase Program, Authorized Amount									$ 4
Treasury Stock, Shares, Acquired			24,600,000			51,600,000
Treasury Stock, Value, Acquired			$ 674			$ 1,488
The 2018 Repurchase Program [Member]
Stock Repurchase Program, Authorized Amount								$ 2,000
Treasury Stock, Shares, Acquired	4,800,000				12,600,000
Treasury Stock, Value, Acquired	$ 151				$ 395
2019 Repurchase Authorization [Member] | Subsequent Event [Member]
Stock Repurchase Program, Authorized Amount							$ 5,000
Common Stock [Member]
Convertible Preferred Stock, Shares Issued upon Conversion	50,000				50,000
Series A Convertible Preferred Stock [Member]
Convertible Preferred Stock, Shares Issued upon Conversion	2,300				2,300