Summary of Significant Accounting Policies - Pension and Other Post-retirement Benefit Costs (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Unrecognized actuarial losses in AOCI	$ 17.2	$ 0.0	$ 0.0	$ 17.2