Leases (Schedule of Lease Assets and Liabilities Recorded in Consolidated Balance Sheets) (Detail) - USD ($) $ in Millions		Dec. 31, 2021		Dec. 31, 2020		Jan. 01, 2019
Leases [Abstract]
Operating lease assets		$ 19	[1]	$ 21	[1]	$ 19
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]		us-gaap:OtherAssets		us-gaap:OtherAssets
Finance lease assets	[2]	$ 13		$ 20
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]		Utility plant, net		Utility plant, net
Total lease assets		$ 32		$ 41
Operating lease liabilities - current	[3]	2		3
Operating lease liabilities - noncurrent	[4]	17		18
Finance lease liabilities - current	[5]	$ 5		$ 6
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]		Liabilities Current		Liabilities Current
Finance lease liabilities - noncurrent		$ 10		$ 15
Total lease liabilities		$ 34		$ 42

[1] Included in other deferred debits and other assets in the Consolidated Balance Sheets.

[2] Included in utility plant, net, in the Consolidated Balance Sheets, net of $20 million and $24 million of accumulated amortization at December 31, 2021 and December 31, 2020, respectively.

[3] Included in other current liabilities in the Consolidated Balance Sheets.

[4] Included in other deferred credits and other liabilities in the Consolidated Balance Sheets.

[5] Included in securities due within one year in the Consolidated Balance Sheets.