Employee Benefit Plans - Pre-tax Amounts Recorded in AOCI (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial gain (loss)	$ (239.2)	$ (230.6)
Net prior service credit (cost)	(1.2)	(1.2)
Total amounts recorded	(240.4)	(231.8)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial gain (loss)	19.3	31.3
Net prior service credit (cost)	4.7	6.2
Total amounts recorded	$ 24.0	$ 37.5