Variable Interest Entities (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Assets	$ 27,178	$ 27,743
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Assets	109	109
Refined Coal Facility [Member]
Variable Interest Entity [Line Items]
Equity method investments impairment charges	7
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Aggregate investment balance	285	309
Variable Interest Entity, Not Primary Beneficiary [Member] \| Investment In Low Income Housing Properties [Member]
Variable Interest Entity [Line Items]
Equity method investments debt balance	256	269
Variable Interest Entity, Not Primary Beneficiary [Member] \| Trust For Final Capping, Closure, Post-closure Or Environmental Remediation Obligations [Member]
Variable Interest Entity [Line Items]
Value of unconsolidated VIEs	$ 94	$ 101

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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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.

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Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

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