Capital Stock (Details 2) - Class A - USD ($) $ / shares in Units, $ in Millions	1 Months Ended					2 Months Ended		12 Months Ended
	Nov. 30, 2015	Aug. 31, 2015	Jun. 30, 2015	May. 31, 2014	Jan. 31, 2014	Dec. 17, 2015	Jun. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Oct. 31, 2011
Shares purchased outside of stock repurchase program
Total cost of shares purchased outside of publicly announced stock repurchase program								$ 10.4	$ 4.9
Performance shares
Shares purchased outside of stock repurchase program
Shares purchased outside of publicly announced stock repurchase program for share-based compensation awards (in shares)								111,535	64,398
Other stock based awards
Shares purchased outside of stock repurchase program
Total cost of shares purchased outside of publicly announced stock repurchase program		$ 0.2			$ 0.2
Average price per share for shares purchased (in dollars per share)		$ 86.24			$ 71.93
Other stock based awards | Performance shares
Shares purchased outside of stock repurchase program
Shares purchased outside of publicly announced stock repurchase program for share-based compensation awards (in shares)		2,800			2,800
Stock compensation plan for outside directors
Shares purchased outside of stock repurchase program
Total cost of shares purchased outside of publicly announced stock repurchase program	$ 1.1			$ 0.6		$ 9.0
Average price per share for shares purchased (in dollars per share)	$ 87.03			$ 76.45		$ 94.99
Stock compensation plan for outside directors | Performance shares
Shares purchased outside of stock repurchase program
Shares purchased outside of publicly announced stock repurchase program for share-based compensation awards (in shares)	12,230			7,227		94,938
Long-term incentive plan
Shares purchased outside of stock repurchase program
Total cost of shares purchased outside of publicly announced stock repurchase program			$ 0.1				$ 4.1
Average price per share for shares purchased (in dollars per share)			$ 81.91				$ 76.21
Long-term incentive plan | Performance shares
Shares purchased outside of stock repurchase program
Shares purchased outside of publicly announced stock repurchase program for share-based compensation awards (in shares)			1,567				54,371
Stock repurchase program
Stock repurchases
Shares repurchased under stock repurchase program (in shares)								0	272,057
Total cost of shares repurchased under stock repurchase program									$ 19.2
Amount of authorized stock repurchases approved for continuation under the current program										$ 150.0
Approximate amount of repurchase authority remaining under the current stock repurchase program								$ 17.8