Shareholders' Equity - Restricted Stock Awards (Details) - Restricted Stock - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unvested Restricted Stock Outstanding
Balance at the beginning of the period (in shares)	0.1	0.3	1.2
Granted (in shares)	0.0	0.0	0.0
Vested (in shares)	0.0	(0.2)	(0.2)
Forfeited (in shares)	0.0	(0.1)	(0.7)
Balance at the end of the period (in shares)	0.0	0.1	0.3	1.2
Weighted Average Grant date Fair Value Price
Balance at the beginning of the period (in dollars per share)	$ 43.63	$ 45.80	$ 43.10
Granted (in dollars per share)	0	0	0
Vested (in dollars per share)	45.35	47.48	43.69
Forfeited (in dollars per share)	51.47	44.77	41.50
Balance at the end of the period (in dollars per share)	$ 41.56	$ 43.63	$ 45.80	$ 43.10
Aggregate Intrinsic Value	$ 1.3	$ 1.4	$ 9.7	$ 55.7
Weighted Average Remaining Vesting Term	8 months 12 days	1 year	10 months 24 days	9 months 18 days
Aggregate value of awards vested	$ 1.0	$ 3.8	$ 7.8