Capital Stock - Schedule of Common Stock Outstanding (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common stock:
Balance, beginning of year	106.0	104.8	104.0
Activity under stock plans	0.7	1.2	0.8
Balance, end of year	106.7	106.0	104.8
Treasury stock:
Balance, beginning of year	12.5	9.3	5.1
Repurchased	2.8	3.2	4.2
Balance, end of year	15.3	12.5	9.3
Common stock outstanding	91.4	93.5	95.5