Postretirement Benefit Plans (Weighted-Average Asset Allocation By Investment Category) (Details) - Scottdale Defined Benefit Pension Plan [Member]	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, Weighted-average asset allocation percent	100.00%	100.00%
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, Weighted-average asset allocation percent	10.57%	51.76%
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, Weighted-average asset allocation percent	58.45%	35.23%
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, Weighted-average asset allocation percent	30.98%	13.01%