Capital Stock (Textuals) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
Capital Stock (Textuals) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Aug. 24, 2015
Equity, Class of Treasury Stock [Line Items]
Shares repurchased (less than $1 million)		$ 60		$ 50
Share Repurchase Programs
Equity, Class of Treasury Stock [Line Items]
Shares repurchased (in shares - less than 0.1 million)	100,000		100,000		700,000	800,000
Shares repurchased (less than $1 million)	$ 1		$ 1		$ 68	$ 60
2015 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount							$ 500
Shares repurchased (in shares - less than 0.1 million)	0				600,000	700,000
Shares repurchased (less than $1 million)					$ 60	$ 50
Remaining authorized amount of repurchase	$ 228				$ 228
Settlement of Employee Tax Withholding Obligations
Equity, Class of Treasury Stock [Line Items]
Shares repurchased (in shares - less than 0.1 million)	100,000		100,000		100,000	100,000
Shares repurchased (less than $1 million)	$ 1		$ 1		$ 8	$ 10