Capital Stock (Tables)

12 Months Ended

Dec. 31, 2018

Stockholders Equity Note [Abstract]

Schedule of Common Stock Outstanding

Common stock outstanding as of December 31, 2018, 2017 and 2016 was as follows:

(Number of shares in millions)	2018		2017		2016
Common stock:
Balance, beginning of year	107.8			106.7		106.0
Activity under stock plans	0.7		1.1		0.7
Balance, end of year	108.5			107.8		106.7
Treasury stock:
Balance, beginning of year	18.2		15.3		12.5
Repurchased		5.5	2.9		2.8
Balance, end of year	23.7		18.2		15.3
Common stock outstanding	84.8		89.6		91.4