Employee Retirement Plans - Summary of Plans' Weighted-Average Asset Targets and Actual Allocations as Percentage of Plan Assets (Details)	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Target Allocations (as a percent)	100.00%
Actual Allocations (as a percent)	100.00%
Liability hedging
Defined Benefit Plan Disclosure [Line Items]
Target Allocations (as a percent)	29.90%
Actual Allocations (as a percent)	37.10%
Equities
Defined Benefit Plan Disclosure [Line Items]
Target Allocations (as a percent)	12.90%
Actual Allocations (as a percent)	6.90%
Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Target Allocations (as a percent)	29.40%
Actual Allocations (as a percent)	36.30%
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Target Allocations (as a percent)	20.80%
Actual Allocations (as a percent)	18.10%
Property
Defined Benefit Plan Disclosure [Line Items]
Target Allocations (as a percent)	6.10%
Actual Allocations (as a percent)	1.60%
Other
Defined Benefit Plan Disclosure [Line Items]
Target Allocations (as a percent)	0.90%
Actual Allocations (as a percent)		0.00%