Pension and Other Post-Retirement Benefits - Fair Value Pension Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair value of pension plan assets
Assets	$ 369.8	$ 435.6
Short-term investment funds [Member]
Fair value of pension plan assets
Assets	0.7	2.6
Common stock collective funds [Member]
Fair value of pension plan assets
Assets	148.2	204.1
Fixed income collective trust funds [Member]
Fair value of pension plan assets
Assets	207.1	211.0
Real estate investment funds [Member]
Fair value of pension plan assets
Assets	13.8	14.8
Loan Fund [Member]
Fair value of pension plan assets
Assets	$ 0.0	$ 3.1