Net Income Per Share Attributable To Common Stockholders (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock	$ 653,000,000	$ 179,000,000	$ 36,000,000
Stock repurchase program
Equity, Class of Treasury Stock [Line Items]
Authorized repurchase amount	2,000,000,000
Repurchase of common stock		127,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	1,300,000,000
Shares repurchased
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock	$ 622,000,000	149,000,000	$ 0
Previously Authorized Common Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock		$ 22,000,000