Income Taxes - Quarter information (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Income Taxes
Effective tax rate of income (loss) before income taxes	22.70%	17.00%
Equity in net losses of unconsolidated entities	$ 9	$ 26
Excess tax benefits associated with equity-based compensation	9	21
Increase (decrease) to accruals and related deferred taxes		(6)
Asset impairments	6
Investments Qualifying for Federal Tax Credits [Member]
Income Taxes
Equity in net losses of unconsolidated entities	9	26
Income tax (expense) benefit, including tax credits, from equity method investment	16	24
Refined Coal Facility [Member]
Income Taxes
Equity method investments impairment charges		7
Investment In Low Income Housing Properties [Member]
Income Taxes
Interest expense	$ 2	$ 3

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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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 of income (loss) for proportionate share of equity method investee's income (loss).

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The increase (decrease) during the period in the amount due for taxes based on the reporting entity's earnings or attributable to the entity's income earning process (business presence) within a given jurisdiction.

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Amount of the cost of borrowed funds accounted for as interest expense.

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Income tax expense (benefit), including federal tax credits, from equity method investment.

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Income Taxes [Line Items]

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