Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended		134 Months Ended
		Apr. 18, 2019	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Aggregate Board of Directors repurchase authorizations (in $ millions)	[1]		$ 0	$ 0	$ 3,866
Stock Repurchase Program, Remaining Authorized Repurchase Amount			$ 513		$ 513
Common stock, par value			$ 0.0001		$ 0.0001	$ 0.0001
Subsequent Event [Member]
Class of Stock [Line Items]
Aggregate Board of Directors repurchase authorizations (in $ millions)	[1]	$ 1,500
Common Stock, Dividends, Per Share, Declared		$ 0.62
Dividends, Common Stock, Cash		$ 78

[1] These authorizations give management discretion in determining the timing and conditions under which shares may be repurchased. This repurchase program began in February 2008 and does not have an expiration date.