Pension Plans And Other Postretirement Benefits (Components Of Net Periodic Benefit Costs) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 763	$ 680	$ 1,526	$ 1,360
Interest cost	2,540	2,954	5,080	5,908
Expected return on plan assets	(3,938)	(3,818)	(7,876)	(7,636)
Amortization of prior service cost	148	155	296	310
Amortization of actuarial loss	1,992	1,982	3,984	3,964
Net periodic benefit (income) cost	1,505	1,953	3,010	3,906
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	217	205	434	410
Interest cost	677	750	1,354	1,500
Expected return on plan assets	(675)	(621)	(1,350)	(1,242)
Amortization of prior service cost	(116)	(116)	(232)	(232)
Amortization of actuarial loss	156	166	312	332
Net periodic benefit (income) cost	259	$ 384	518	768
Peoples Gas Acquisition [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	226		266
Interest cost	1,090		1,281
Expected return on plan assets	(1,719)		(2,021)
Net periodic benefit (income) cost	(403)		$ (474)
Peoples Gas Acquisition [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	441			518
Interest cost	309			363
Expected return on plan assets	(432)			(507)
Net periodic benefit (income) cost	$ 318			$ 374