Summary of Fair Value of Plan Assets by Asset Category (Parenthetical) (Details)	Dec. 31, 2019	Dec. 31, 2018
Bonds | Balanced Fund
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	42.00%	19.00%
Bonds | Fixed Income
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	92.00%	86.00%
Equity Securities | Balanced Fund
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	32.00%	42.00%
Other Asset | Balanced Fund
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	19.00%	38.00%
Other Asset | Fixed Income
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	5.00%
Cash | Balanced Fund
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	7.00%	1.00%
Cash | Fixed Income
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	3.00%	14.00%