Employee Benefit Plans Expected Benefit Payments (Details) $ in Millions	Dec. 31, 2020 USD ($)
Pension Plan | UNITED STATES
Defined Benefit Plans and Other Postretirement Benefit Plans
Benefit Payments in Year One	$ 75.0
Benefit Payments in Year Two	78.4
Benefit Payments in Year Three	82.2
Benefit Payments in Year Four	86.1
Benefit Payments in Year Five	90.1
Benefit Payments in Five Fiscal Years Thereafter	514.9
Pension Plan | UNITED KINGDOM
Defined Benefit Plans and Other Postretirement Benefit Plans
Benefit Payments in Year One	6.1
Benefit Payments in Year Two	6.1
Benefit Payments in Year Three	6.5
Benefit Payments in Year Four	7.0
Benefit Payments in Year Five	7.2
Benefit Payments in Five Fiscal Years Thereafter	42.3
Other Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Benefit Payments in Year One	11.1
Prescription Drug Subsidy Receipts in Year One	0.1
Net OPEB Payments in Year One	11.0
Benefit Payments in Year Two	10.5
Prescription Drug Subsidy Receipts in Year Two	0.1
Net OPEB Payments in Year Two	10.4
Benefit Payments in Year Three	10.0
Prescription Drug Subsidy Receipts in Year Three	0.1
Net OPEB Payments in Year Three	9.9
Benefit Payments in Year Four	9.5
Prescription Drug Subsidy Receipts in Year Four	0.1
Net OPEB Payments in Year Four	9.4
Benefit Payments in Year Five	9.0
Prescription Drug Subsidy Receipts in Year Five	0.1
Net OPEB Payments in Year Five	8.9
Benefit Payments in Five Fiscal Years Thereafter	38.3
Prescription Drug Subsidy Receipts in Five Fiscal Years Thereafter	0.2
Net OPEB Payments in Five Fiscal Years Thereafter	$ 38.1