Pension Benefits, Other Postretirement Benefits and Employee Savings and Investment Plans (Summary of Changes in Fair Value of Guaranteed Deposit Account's Level 3 Assets) (Details) - Pension Benefits $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets as of January 1	$ 42,835
Fair value of plan assets as of December 31	35,296
Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets as of January 1	1,338
Fair value of plan assets as of December 31	1,347
Guaranteed deposit account
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets as of January 1	1,338
Fair value of plan assets as of December 31	1,347
Guaranteed deposit account | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets as of January 1	1,338
Change in unrealized gain (loss)	34
Purchases, sales, issuances and settlements (net)	(25)
Fair value of plan assets as of December 31	$ 1,347