Capital Stock (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Aug. 24, 2015	Aug. 20, 2013	Aug. 18, 2012
Equity, Class of Treasury Stock [Line Items]
Shares repurchased (in shares) (less than 0.1 million shares in the three months ended September 30, 2015 and three and six months ended September 30, 2014, repurchased outside of repurchase programs)	100,000	100,000.0	100,000	100,000
Shares repurchased (in dollars) (less than $1 million in the three months ended September 30, 2015 and 2014, repurchased outside of repurchase programs)	$ 1.0	$ 1.0	$ 3.0	$ 2.0
2015 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount					$ 500.0
Shares repurchased (in shares) (less than 0.1 million shares in the three months ended September 30, 2015 and three and six months ended September 30, 2014, repurchased outside of repurchase programs)	900,000		900,000
Shares repurchased (in dollars) (less than $1 million in the three months ended September 30, 2015 and 2014, repurchased outside of repurchase programs)	$ 30.0		$ 30.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 470.0		$ 470.0
2013 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount						$ 250.0
Shares repurchased (in shares) (less than 0.1 million shares in the three months ended September 30, 2015 and three and six months ended September 30, 2014, repurchased outside of repurchase programs)	600,000	800,000	2,000,000	3,400,000
Shares repurchased (in dollars) (less than $1 million in the three months ended September 30, 2015 and 2014, repurchased outside of repurchase programs)	$ 20.0	$ 30.0	$ 70.0	$ 130.0
2012 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount							$ 2.0
Shares repurchased (in shares) (less than 0.1 million shares in the three months ended September 30, 2015 and three and six months ended September 30, 2014, repurchased outside of repurchase programs)	800,000	0	800,000	0
Shares repurchased (in dollars) (less than $1 million in the three months ended September 30, 2015 and 2014, repurchased outside of repurchase programs)	$ 25.0		$ 25.0
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	200,000		200,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 8.0		$ 8.0