Retirement Benefits - Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Subsidiaries [Member]
Defined Benefit Plan and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer matching contribution, percent	4.50%
Defined Contribution Plan, Interest Credit	4.00%
Subsidiaries [Member] | employer contribution [Member]
Defined Benefit Plan and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer matching contribution, percent	4.00%
Subsidiaries [Member] | employer contribution [Member] | Collective Bargaining Arrangement Member [Member]
Defined Benefit Plan and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer matching contribution, percent	4.00%
Subsidiaries [Member] | employer contribution [Member] | Collective Bargaining Arrangement Member [Member] | UA represented [Member]
Defined Benefit Plan and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer matching contribution, percent	4.00%
Subsidiaries [Member] | employer contribution [Member] | Collective Bargaining Arrangement Member [Member] | IBEW represented [Member]
Defined Benefit Plan and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer matching contribution, percent	4.00%
Other Pension Plan [Member]
Defined Benefit Plan and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss (gain)	$ 1,164	$ (715)
Amortization of net (loss) gain	39	82
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax	0	0
Prior service cost (credit)	205	44
Amortization of prior service (cost) credit	6	0
Total change in other comprehensive income for year	(926)	841
Other Pension Plan [Member] | Subsidiaries [Member]
Defined Benefit Plan and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss (gain)	1,164	(715)
Amortization of net (loss) gain	53	137
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax	0	0
Prior service cost (credit)	205	44
Amortization of prior service (cost) credit	6	0
Total change in other comprehensive income for year	(912)	896
Qualified Plan | Pension Plan [Member]
Defined Benefit Plan and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss (gain)	61,348	(11,851)
Amortization of net (loss) gain	(11,803)	(8,160)
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax	0	0
Prior service cost (credit)	0	0
Amortization of prior service (cost) credit	(1,904)	(1,980)
Total change in other comprehensive income for year	(71,247)	5,671
Qualified Plan | Pension Plan [Member] | Subsidiaries [Member]
Defined Benefit Plan and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss (gain)	61,345	(11,858)
Amortization of net (loss) gain	(21,862)	(19,043)
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax	0	0
Prior service cost (credit)	0	0
Amortization of prior service (cost) credit	(1,513)	(1,573)
Total change in other comprehensive income for year	(81,694)	(5,612)
Nonqualified Plan | Pension Plan [Member]
Defined Benefit Plan and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss (gain)	(828)	(3,663)
Amortization of net (loss) gain	(2,164)	(2,122)
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax	830	(4,806)
Prior service cost (credit)	0	0
Amortization of prior service (cost) credit	349	349
Total change in other comprehensive income for year	(2,515)	(3,614)
Nonqualified Plan | Pension Plan [Member] | Subsidiaries [Member]
Defined Benefit Plan and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss (gain)	(828)	(3,663)
Amortization of net (loss) gain	(2,343)	(2,385)
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax	886	(5,248)
Prior service cost (credit)	0	0
Amortization of prior service (cost) credit	349	349
Total change in other comprehensive income for year	$ (2,750)	$ (4,319)