Share-Based Compensation Plans - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Options
Options outstanding, number of options (in shares)	1,464	1,534
Granted (in shares)	0	0
Exercised (in shares)	0	(27)
Forfeited or expired (in shares)	(120)	(43)
Options outstanding, number of options (in shares)	1,344	1,464	1,534
Options exercisable (in shares)	1,138
Options expected to vest (in shares)	200
Weighted-Average Exercise Price Per Share
Beginning options outstanding, weighted average exercise price (in dollars per share)	$ 92.33	$ 91.56
Granted (in dollars per share)	0	0
Exercised (in dollars per share)	0	34.30
Forfeited or expired (in dollars per share)	78.21	99.58
Ending options outstanding, weighted average exercise price (in dollars per share)	93.61	$ 92.33	$ 91.56
Options exercisable (in dollars per share)	96.34
Options expected to vest (in dollars per share)	$ 78.51
Weighted- Average Remaining Term in Years	5 years 2 months 12 days	5 years 9 months 18 days
Weighted- Average Remaining Term in Years, Options exercisable	4 years 9 months 18 days
Weighted- Average Remaining Term in Years, Options expected to vest	7 years 1 month 6 days
Aggregate Intrinsic Value	$ 0.0	$ 0.0
Aggregate Intrinsic Value, Options exercisable	0.0
Aggregate Intrinsic Value, Options expected to vest	0.0
Options exercised, aggregate intrinsic value	$ 0.0	$ 0.5	$ 1.1
Options granted, weighted-average grant date fair value (in USD per share)	$ 0	$ 0	$ 24.43