Pension and Other Postretirement Benefits - Schedule of Assumed Health Care Cost Trend Rates (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate assumed for next year	5.50%	5.50%	5.50%
Rate to which the cost trend rate gradually declines	4.50%	4.50%	4.50%
Year that the rate reaches the rate at which it is assumed to remain	2023	2023	2022
Number of years over actual annual healthcare cost trend experience	20 years
Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate to which the cost trend rate gradually declines	(3.80%)
Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate to which the cost trend rate gradually declines	4.00%
Other postretirement benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of years over actual annual healthcare cost trend experience	3 years