Employee Benefit Plans (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected future employer contributions, next fiscal year, description		No
Voluntary retirement program related charges	$ 62
Voluntary retirement program related charges net of taxes	47
Other Operations and Maintenance Expense
Defined Benefit Plan Disclosure [Line Items]
Voluntary retirement program related charges	50
Other Taxes
Defined Benefit Plan Disclosure [Line Items]
Voluntary retirement program related charges	3
Other Income (Expense), Net
Defined Benefit Plan Disclosure [Line Items]
Voluntary retirement program related charges	$ 9

Defined benefit plan cost of providing special or contractual termination benefit recognized during period net of tax.

No definition available.

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- Definition

Defined benefit plan, expected future employer contributions, remainder of fiscal year, description.

+ References

No definition available.

+ Details

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- Definition

Amount of cost of providing special or contractual termination benefits payable from defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (q)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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