Capital Stock - Options outstanding and exercisable (Details) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Information about options outstanding and options exercisable by year of grant
Range of Exercise Prices, Lower Range Limit (USD per share)	$ 7
Range of Exercise Prices, Upper Range Limit (USD per share)	$ 11
Options Granted, Range One [Member]
Information about options outstanding and options exercisable by year of grant
Range of Exercise Prices, Lower Range Limit (USD per share)	$ 10
Range of Exercise Prices, Upper Range Limit (USD per share)	$ 11
2004 – expire in 2014
Information about options outstanding and options exercisable by year of grant
Range of Exercise Prices, Lower Range Limit (USD per share)	$ 10
Range of Exercise Prices, Upper Range Limit (USD per share)	$ 11
2005 – expire in 2015
Information about options outstanding and options exercisable by year of grant
Range of Exercise Prices, Lower Range Limit (USD per share)	$ 10
Range of Exercise Prices, Upper Range Limit (USD per share)	$ 11
2006 – expire in 2016
Information about options outstanding and options exercisable by year of grant
Range of Exercise Prices, Lower Range Limit (USD per share)	$ 9
Range of Exercise Prices, Upper Range Limit (USD per share)	$ 10
2007 – expire in 2015
Information about options outstanding and options exercisable by year of grant
Range of Exercise Prices, Lower Range Limit (USD per share)	$ 7
Range of Exercise Prices, Upper Range Limit (USD per share)	$ 10
Stock Options
Information about options outstanding and options exercisable by year of grant
Average Remaining Term	1 year 5 months 18 days
Options on Shares Outstanding	2,455,495
Options on Shares Exercisable	2,455,495
Options Outstanding, Weighted Average Exercise Price (USD per share)	$ 9.19
Options Exercisable, Weighted Average Exercise Price (USD per share)	$ 9.19
Options Outstanding, Aggregate Intrinsic Value	$ 29.4
Options Exercisable, Aggregate Intrinsic Value	29.4
Stock Options | Options Granted, Range One [Member]
Information about options outstanding and options exercisable by year of grant
Average Remaining Term	4 months 15 days
Options on Shares Outstanding	9,185
Options on Shares Exercisable	9,185
Options Outstanding, Weighted Average Exercise Price (USD per share)	$ 10.05
Options Exercisable, Weighted Average Exercise Price (USD per share)	$ 10.05
Options Outstanding, Aggregate Intrinsic Value	0.1
Options Exercisable, Aggregate Intrinsic Value	0.1
Stock Options | 2004 – expire in 2014
Information about options outstanding and options exercisable by year of grant
Average Remaining Term	9 months 14 days
Options on Shares Outstanding	43,188
Options on Shares Exercisable	43,188
Options Outstanding, Weighted Average Exercise Price (USD per share)	$ 10.90
Options Exercisable, Weighted Average Exercise Price (USD per share)	$ 10.90
Options Outstanding, Aggregate Intrinsic Value	0.4
Options Exercisable, Aggregate Intrinsic Value	0.4
Stock Options | 2005 – expire in 2015
Information about options outstanding and options exercisable by year of grant
Average Remaining Term	1 year 11 months 5 days
Options on Shares Outstanding	49,966
Options on Shares Exercisable	49,966
Options Outstanding, Weighted Average Exercise Price (USD per share)	$ 10.05
Options Exercisable, Weighted Average Exercise Price (USD per share)	$ 10.05
Options Outstanding, Aggregate Intrinsic Value	0.6
Options Exercisable, Aggregate Intrinsic Value	0.6
Stock Options | 2006 – expire in 2016
Information about options outstanding and options exercisable by year of grant
Average Remaining Term	7 months 27 days
Options on Shares Outstanding	565,970
Options on Shares Exercisable	565,970
Options Outstanding, Weighted Average Exercise Price (USD per share)	$ 10.31
Options Exercisable, Weighted Average Exercise Price (USD per share)	$ 10.31
Options Outstanding, Aggregate Intrinsic Value	6.1
Options Exercisable, Aggregate Intrinsic Value	6.1
Stock Options | 2007 – expire in 2015
Information about options outstanding and options exercisable by year of grant
Average Remaining Term	1 year 8 months 28 days
Options on Shares Outstanding	1,787,186
Options on Shares Exercisable	1,787,186
Options Outstanding, Weighted Average Exercise Price (USD per share)	$ 8.76
Options Exercisable, Weighted Average Exercise Price (USD per share)	$ 8.76
Options Outstanding, Aggregate Intrinsic Value	22.2
Options Exercisable, Aggregate Intrinsic Value	$ 22.2