Share-Based Compensation Plans - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Options
Options outstanding, number of options (in shares)	1,072	749
Granted (in shares)	521	439
Exercised (in shares)	(33)	(31)
Forfeited or expired (in shares)	(26)	(85)
Options outstanding, number of options (in shares)	1,534	1,072	749
Options exercisable (in shares)	764
Options expected to vest (in shares)	736
Weighted-Average Exercise Price Per Share
Beginning options outstanding, weighted average exercise price (in dollars per share)	$ 94.90	$ 108.40
Granted (in dollars per share)	82.43	70.34
Exercised (in dollars per share)	42.06	24.75
Forfeited or expired (in dollars per share)	97.82	118.47
Ending options outstanding, weighted average exercise price (in dollars per share)	91.56	$ 94.90	$ 108.40
Options exercisable (in dollars per share)	101.27
Options expected to vest (in dollars per share)	$ 82.12
Weighted- Average Remaining Term in Years	6 years 10 months 24 days	6 years 10 months 24 days
Weighted- Average Remaining Term in Years, Options exercisable	5 years 7 months 6 days
Weighted- Average Remaining Term in Years, Options expected to vest	8 years 1 month 6 days
Aggregate Intrinsic Value	$ 0.1	$ 10.9
Aggregate Intrinsic Value, Options exercisable	0.1
Aggregate Intrinsic Value, Options expected to vest	0.0
Options exercised, aggregate intrinsic value	$ 1.1	$ 1.7	$ 5.2
Options granted, weighted-average grant date fair value (in USD per share)	$ 24.43	$ 19.50	$ 33.53