Capital Stock (Textuals) (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended					9 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Aug. 24, 2015
Equity, Class of Treasury Stock [Line Items]
Shares repurchased (less than $1 million)		$ 25		$ 25	$ 25
Share Repurchase Programs
Equity, Class of Treasury Stock [Line Items]
Shares repurchased (in shares - less than 0.1 million)	0.1					0.5
Shares repurchased (less than $1 million)	$ 1					$ 39
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)	0.0		0.0			0.3	0.7
Shares repurchased (less than $1 million)	$ 0		$ 0			$ 25	$ 50
Remaining authorized amount of repurchase	$ 338					$ 338
Settlement of Employee Tax Withholding Obligations
Equity, Class of Treasury Stock [Line Items]
Shares repurchased (in shares - less than 0.1 million)	0.1		0.1			0.2	0.1
Shares repurchased (less than $1 million)	$ 1		$ 1			$ 14	$ 8