Benefit Plans - Long-Term Target Allocations (Details)	12 Months Ended
	Dec. 31, 2020
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Proportion of U.S. and U.K pension plans in total benefit obligation (as a percent)	80.00%
Proportion of U.S. and U.K pension plans in total plan assets (as a percent)	92.00%
U.S. Plans
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Long-term target allocations (as a percent)	100.00%
U.S. Plans | Cash and cash equivalents
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Long-term target allocations (as a percent)	0.00%
U.S. Plans | Equity
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Long-term target allocations (as a percent)	20.00%
U.S. Plans | Fixed income
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Long-term target allocations (as a percent)	80.00%
U.S. Plans | Real estate and other
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Long-term target allocations (as a percent)	0.00%
UK Plan
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Long-term target allocations (as a percent)	100.00%
UK Plan | Cash and cash equivalents
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Long-term target allocations (as a percent)	0.00%
UK Plan | Equity
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Long-term target allocations (as a percent)	32.00%
UK Plan | Fixed income
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Long-term target allocations (as a percent)	30.00%
UK Plan | Real estate and other
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Long-term target allocations (as a percent)	38.00%