Capital Stock and Share Based Compensation Plans - Summary of stock option transactions (Details)	12 Months Ended
	Dec. 31, 2015 $ / shares shares	Dec. 31, 2014 $ / shares shares	Dec. 31, 2013 $ / shares shares	Dec. 31, 2012 $ / shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding and Exercisable [Roll Forward]
Options outstanding at beginning of period, number of shares | shares	1,703,876	3,370,048	8,011,380
Options exercised in period, number of shares | shares	(877,966)	(1,662,055)	(4,635,148)
Options impact of spin-off, number of shares | shares	170,969
Options forfeited in period, number of shares | shares		(4,117)	(6,184)
Options outstanding at end of period, number of shares | shares		1,703,876	3,370,048
Options exercisable, number of shares | shares	996,879
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding and Exercisable, Weighted Average Exercise Price [Roll Forward]
Options outstanding at beginning of period, weighted-average exercise price (USD per share)	$ 8.92	$ 9.46	$ 9.77
Options exercised in period, weighted-average exercise price (USD per share)	8.85	10.01	10.00
Options impact of spin-off, weighted-average exercise price (USD per share)	7.62
Options forfeited in period, weighted-average exercise price (USD per share)		10.45	10.23
Options outstanding at end of period, weighted-average exercise price (USD per share)	7.45	8.92	9.46
Options Exercisable, Weighted Average Exercise Price (USD per share)	$ 7.45	$ 8.92	$ 9.46	$ 9.77
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding and Exercisable, Exercise Price Range [Roll Forward]
Options outstanding at beginning of period, lower end of range of exercise price range (USD per share)	7	7	7
Options outstanding at beginning of period, upper end of range of exercise price range (USD per share)	11	11	11
Options exercised, lower end of exercise price range (USD per share)	8	9	7
Options exercised, upper end of exercise price range (USD per share)	11	11	11
Options forfeited, lower end of exercise price range (USD per share)		10	9
Options forfeited, upper end of exercise price range (USD per share)		11	11
Options impact of spin-off, lower end of exercise price range (USD per share)	$ 6
Options impact of spin-off, upper end of exercise price range (USD per share)	$ 9
Options outstanding at end of period, lower end of range of exercise price range (USD per share)	6	7	7
Options outstanding at end of period, upper end of range of exercise price range (USD per share)	9	11	11
Options exercisable, lower end of exercise price range (USD per share)	6	7	7
Options exercisable, upper end of exercise price range	9	11	11