Acquisitions (Preliminary Purchase Price Allocation) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Mar. 15, 2020
Business Acquisition [Line Items]
Goodwill	$ 2,340,792	$ 2,340,815	$ 2,324,547
Peoples Gas Acquisition [Member]
Business Acquisition [Line Items]
Property, plant and equipment, net	2,476,551
Current assets	233,334
Regulatory assets	264,458
Goodwill	2,277,447			$ 2,277,447
Other long-term assets	75,071
Total assets acquired	5,326,861
Current portion of long-term debt	5,136
Loans payable	181,000
Other current liabilities	185,920
Long-term debt	999,460
Deferred income taxes	193,125
Regulatory liabilities	129,418
Other long-term liabilities	167,458
Total liabilities assumed	1,861,517
Net assets acquired	3,465,344
Amounts Previously Recognized [Member] | Peoples Gas Acquisition [Member]
Business Acquisition [Line Items]
Property, plant and equipment, net	2,476,551
Current assets	242,531
Regulatory assets	286,751
Goodwill	2,261,047
Other long-term assets	75,071
Total assets acquired	5,341,951
Current portion of long-term debt	5,136
Loans payable	181,000
Other current liabilities	186,120
Long-term debt	999,460
Deferred income taxes	213,647
Regulatory liabilities	123,029
Other long-term liabilities	168,215
Total liabilities assumed	1,876,607
Net assets acquired	3,465,344
Measurement Period Adjustments [Member] | Peoples Gas Acquisition [Member]
Business Acquisition [Line Items]
Current assets	(9,197)
Regulatory assets	(22,293)
Goodwill	16,400
Total assets acquired	(15,090)
Other current liabilities	(200)
Deferred income taxes	(20,522)
Regulatory liabilities	6,389
Other long-term liabilities	(757)
Total liabilities assumed	$ (15,090)