Retirement and Other Postretirement Benefit Plans - Schedule of Pension Assets Measured at Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	$ 233.8	$ 214.3
Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	17.2	28.2
Diversified Growth Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	69.0	55.6
Fixed Income Gilts
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements		19.9
Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	94.9	4.4
Liability Driven Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	48.0	29.7
Index Linked Gilts
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements		73.5
Diversified Investment, Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	2.5	2.4
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	2.2	0.6
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	2.2	0.6
Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	2.2	0.6
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	134.2	206.9
Level 2 | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	17.2	28.2
Level 2 | Diversified Growth Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	69.0	55.6
Level 2 | Fixed Income Gilts
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements		19.9
Level 2 | Liability Driven Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	48.0	29.7
Level 2 | Index Linked Gilts
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements		73.5
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	97.4	6.8	$ 6.2
Actual return on plan assets	0.3	0.4
Purchases, sales and settlements	88.2	0.3
Currency translation adjustments	2.1	(0.1)
Level 3 | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	94.9	4.4	4.2
Actual return on plan assets	0.2	0.1
Purchases, sales and settlements	88.4	0.2
Currency translation adjustments	1.9	(0.1)
Level 3 | Diversified Investment, Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value measurements	2.5	2.4	$ 2.0
Actual return on plan assets	0.1	0.3
Purchases, sales and settlements	(0.2)	$ 0.1
Currency translation adjustments	$ 0.2