Capital Stock - Additional Information (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended			1 Months Ended	9 Months Ended	6 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2014	Sep. 30, 2014	Jun. 30, 2013	Jul. 31, 2013
Equity Class Of Treasury Stock [Line Items]
Aggregate shares repurchased	4,200,000	2,600,000	300,000
Total cost of shares repurchased	$ 175.7	$ 89.5	$ 8.1
2014 Repurchase Plan
Equity Class Of Treasury Stock [Line Items]
Additional authorized amount of outstanding common stock to be repurchased				150
Aggregate shares repurchased					3,993,401
Total cost of shares repurchased					160.0
Remaining amount of authorized under 2014 Repurchase Plan	100
2013 Repurchase Plan
Equity Class Of Treasury Stock [Line Items]
Authorized amount to repurchase outstanding common stock							150
2012 Repurchase Plan
Equity Class Of Treasury Stock [Line Items]
Authorized amount to repurchase outstanding common stock			50
Aggregate shares repurchased						1,573,588
Total cost of shares repurchased						$ 50.0