Share-based Compensation Plans (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	$ 13.8	$ 18.9	$ 20.9
Income tax benefit from compensation cost	$ 1.7	$ 2.7	$ 3.0
Shares [Roll Forward]
Restricted stock outstanding at end of period (in shares)	4,100,000
Restricted Stock/Restricted Stock Units
Weighted average grant date fair market value [Abstract]
Restricted stock outstanding at end of period (in dollars per share)	$ 12.81
Granted (in dollars per share)	13.62	$ 11.92	$ 15.69
Vested (in dollars per share)	11.67
Forfeited (in dollars per share)	13.24
Restricted stock outstanding at end of period (in dollars per share)	$ 13.57	$ 12.81
Shares [Roll Forward]
Restricted stock outstanding at beginning of period (in shares)	4,150,394
Granted (in shares)	1,672,060
Vested (in shares)	(1,564,843)
Forfeited (in shares)	(118,368)
Restricted stock outstanding at end of period (in shares)	4,139,243	4,150,394
Additional disclosures [Abstract]
Total fair value of restricted stock vested	$ 20.4	$ 13.7	$ 19.1
Unrecognized compensation cost	$ 25.8
RSUs subject to performance conditions
Shares [Roll Forward]
Restricted stock outstanding at end of period (in shares)	3,100,000
Additional disclosures [Abstract]
Unrecognized compensation cost	$ 19.8
RSUs subject only to service conditions
Shares [Roll Forward]
Restricted stock outstanding at end of period (in shares)	1,000,000.0
Additional disclosures [Abstract]
Unrecognized compensation cost	$ 5.9
Weighted-average period for recognition of compensation cost	1 year 8 months 12 days
2020 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares can be awarded under the plan (in shares)	11,000,000.0
Shares available for future grants (in shares)	11,100,000
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years