Retirement and Other Postretirement Benefit Plans - Schedule of Impact of One-Percentage-Point Change in Expected Long-term Rate of Return and Discount Rate on Pension Expense and Retirement Obligation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
U.S. Non-qualified Defined Benefit Retirement Plans
Impact of one-percentage-point increase and a one-percentage-point decrease in the expected long-term rate of return and discount rate on periodic pension expense in next fiscal year
One-percentage-point decrease in discount rate	$ 0.1
Impact of one-percentage-point increase and a one-percentage-point decrease in the discount rate on retirement obligation as of December 31, 2019
One-percentage-point increase in discount rate	(0.8)
One-percentage-point decrease in discount rate	0.9
U.S. Retiree Medical Plans
Impact of one-percentage-point increase and a one-percentage-point decrease in the discount rate on retirement obligation as of December 31, 2019
One-percentage-point increase in discount rate	(0.1)
One-percentage-point decrease in discount rate	0.1
United Kingdom defined benefit Retirement plan (the U.K. Plan)
Impact of one-percentage-point increase and a one-percentage-point decrease in the expected long-term rate of return and discount rate on periodic pension expense in next fiscal year
One-percentage-point increase in expected long-term rate of return	(1.4)
One-percentage-point increase in discount rate	(0.3)
One-percentage-point decrease in expected long-term rate of return	1.4
One-percentage-point decrease in discount rate	0.2
Impact of one-percentage-point increase and a one-percentage-point decrease in the discount rate on retirement obligation as of December 31, 2019
One-percentage-point increase in discount rate	(21.6)
One-percentage-point decrease in discount rate	$ 29.0