Capital Stock - Schedule of Common Stock Outstanding (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 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