Employee Stock Compensation Plans - Stock Options (Details) - Stock Options [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, Beginning balance, Shares Under Option (in shares)	629
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures	0
Vested, Shares Under Option (in shares)	(117)
Outstanding, Ending balance, Shares Under Option (in shares)	475	629
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period	37
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, Beginning balance, Weighted Average Exercise Price per Share (in dollars per share)	$ 17.69
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	0.00
Vested, Weighted Average Exercise Price per Share (in dollars per share)	20.48
Outstanding, Ending balance, Weighted Average Exercise Price per Share (in dollars per share)	16.70	$ 17.69
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 21.54
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, Weighted Average Remaining Contratual Term (in years)	1 year 10 months 15 days
Outstanding, Aggregate Intrinsic Value	$ 8.2
Exercisable, Shares Under Option (in shares)	475
Exercisable, Weighted Average Exercise Price per Share (in dollars per share)	$ 16.70
Exercisable, Weighted Average Remaining Contractual Term (in years)	1 year 10 months 15 days
Exercisable, Aggregate Intrinsic Value	$ 8.2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]
Fully vested and expected to vest, Shares Under Option (in shares)	475
Fully vested and expected to vest, Weighted Average Exercise Price per Share (in dollars per share)	$ 16.70
Fully vested and expected to vest, Weighted Average Remaining Contractual Term (in years)	1 year 10 months 15 days
Fully vested and expected to vest, Aggregate Intrinsic Value	$ 8.2
Total intrinsic value of all options exercised	3.0	$ 6.0	$ 6.0
Cash received from option exercises	2.0	8.0	8.0
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options	$ 1.0	$ 2.0	$ 2.0
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]
Vesting period	1 year
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]
Vesting period	10 years