Stockholders' Equity (Repurchases of Common Stock Under Share Repurchase Programs) (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity, Class of Treasury Stock [Line Items]
Total Share Repurchases	$ 869	$ 1,418	$ 885
Total Share Repurchases	4.8	7.2	5.5
Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Total Share Repurchases	$ 800	$ 1,325	$ 800
Total Share Repurchases	4.4	6.7	4.9
Satisfy tax withholding [Member]
Equity, Class of Treasury Stock [Line Items]
Total Share Repurchases	$ 69	$ 93	$ 85
Total Share Repurchases	0.4	0.5	0.6