Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2021 USD ($) Segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 09, 2020 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment	2
Percentage of original cost of depreciable property	3.50%	3.20%	3.40%
Depreciation expense	$ 408,000,000	$ 381,000,000	$ 359,000,000
Allowance for funds used during construction rate	6.46%	6.46%	6.46%
Allowance for funds used during construction	$ 66,000,000	$ 44,000,000	$ 16,000,000
Receivables from contracts with customers	252,000,000	214,000,000
Unbilled revenues	74,000,000	73,000,000
Franchise fees and gross receipts taxes	$ 129,000,000	109,000,000	$ 117,000,000
Natural Gas Contracts [Member]
Summary Of Significant Accounting Policies [Line Items]
Maximum length of time hedging in future cash flow	Nov. 30, 2018
Natural Gas Storage and Transportation [Member]
Summary Of Significant Accounting Policies [Line Items]
Derivative Liabilities	$ 0	0
Derivative Assets	$ 0	$ 0
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Discount rates used in estimating other self-insurance liabilities	1.63%	2.43%
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Discount rates used in estimating other self-insurance liabilities	4.00%	4.00%
Intangible Software Assets [Member]
Summary Of Significant Accounting Policies [Line Items]
Accumulated depreciation and amortization reserve surplus				$ 16,000,000
PGS [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for funds used during construction rate	6.00%	5.97%