Pension and Other Post-Retirement Benefits - Fair Value Pension Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair value of pension plan assets
Assets	$ 432.7	$ 369.8
Short-term investment funds [Member]
Fair value of pension plan assets
Assets	5.9	0.7
Common stock collective funds [Member]
Fair value of pension plan assets
Assets	181.3	148.2
Fixed income collective trust funds [Member]
Fair value of pension plan assets
Assets	232.4	207.1
Real estate investment funds [Member]
Fair value of pension plan assets
Assets	$ 13.1	$ 13.8