Retirement and Other Postretirement Benefit Plans - Schedule of Actual Allocations for the Pension Assets and Target Allocations by Asset Class (Details)	Dec. 31, 2020	Dec. 31, 2019
Change in plan assets:
Percentage of Plan Assets	100.00%	100.00%
Target Allocations	100.00%	100.00%
Diversified Growth Funds
Change in plan assets:
Percentage of Plan Assets	29.50%	25.90%
Target Allocations	27.10%	22.30%
Index Linked Gilts
Change in plan assets:
Percentage of Plan Assets		34.30%
Target Allocations		33.40%
Fixed Interest Gilts
Change in plan assets:
Percentage of Plan Assets		9.30%
Target Allocations		9.10%
Liability Driven Investments
Change in plan assets:
Percentage of Plan Assets	20.50%	13.80%
Target Allocations	23.90%	16.50%
All Other Regions Equity Fund
Change in plan assets:
Percentage of Plan Assets	5.10%	9.20%
Target Allocations	5.10%	10.80%
U.K. Equity Fund
Change in plan assets:
Percentage of Plan Assets	2.20%	4.00%
Target Allocations	2.20%	4.70%
Diversified Investment, Funds
Change in plan assets:
Percentage of Plan Assets	1.10%	1.10%
Target Allocations	1.10%	1.10%
Insurance contracts
Change in plan assets:
Percentage of Plan Assets	40.60%	2.00%
Target Allocations	40.60%	2.10%
Cash and Cash Equivalents
Change in plan assets:
Percentage of Plan Assets	1.00%	0.40%