Employee Benefit Obligations - Asset Categories (Details)	Dec. 31, 2021	Dec. 31, 2020
United States | Minimum | Fixed income securities
Target asset allocations
Target asset allocations (as a percent)	24.00%
United States | Minimum | Equity securities
Target asset allocations
Target asset allocations (as a percent)	26.00%
United States | Minimum | Alternative investments
Target asset allocations
Target asset allocations (as a percent)	5.00%
United States | Maximum | Fixed income securities
Target asset allocations
Target asset allocations (as a percent)	58.00%
United States | Maximum | Equity securities
Target asset allocations
Target asset allocations (as a percent)	54.00%
United States | Maximum | Alternative investments
Target asset allocations
Target asset allocations (as a percent)	19.00%
United Kingdom | Minimum | Fixed Income Securities And Cash And Cash Equivalents Combined
Target asset allocations
Target asset allocations (as a percent)	60.00%
United Kingdom | Minimum | Cash and cash equivalents
Target asset allocations
Target asset allocations (as a percent)	60.00%
United Kingdom | Minimum | Fixed income securities
Target asset allocations
Target asset allocations (as a percent)	60.00%
United Kingdom | Minimum | Equity securities
Target asset allocations
Target asset allocations (as a percent)	0.00%
United Kingdom | Minimum | Alternative investments
Target asset allocations
Target asset allocations (as a percent)	0.00%
United Kingdom | Maximum | Fixed Income Securities And Cash And Cash Equivalents Combined
Target asset allocations
Target asset allocations (as a percent)	100.00%
United Kingdom | Maximum | Cash and cash equivalents
Target asset allocations
Target asset allocations (as a percent)	100.00%
United Kingdom | Maximum | Fixed income securities
Target asset allocations
Target asset allocations (as a percent)	100.00%
United Kingdom | Maximum | Equity securities
Target asset allocations
Target asset allocations (as a percent)	15.00%
United Kingdom | Maximum | Alternative investments
Target asset allocations
Target asset allocations (as a percent)	5.00%
Defined Benefit Pension Plans
Target asset allocations
Weighted average asset allocations (as a percent)	100.00%	100.00%
Defined Benefit Pension Plans | Cash and cash equivalents
Target asset allocations
Weighted average asset allocations (as a percent)		1.00%
Defined Benefit Pension Plans | Fixed income securities
Target asset allocations
Weighted average asset allocations (as a percent)	81.00%	79.00%
Defined Benefit Pension Plans | Equity securities
Target asset allocations
Weighted average asset allocations (as a percent)	17.00%	17.00%
Defined Benefit Pension Plans | Alternative investments
Target asset allocations
Weighted average asset allocations (as a percent)	2.00%	3.00%