Debt and Other Financing Arrangements - Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ 92		$ 82
Other assets
Debt Instrument [Line Items]
Amortization of debt issuance fees	2	$ 1
Unamortized debt issuance costs	15		$ 17
Interest Expense
Debt Instrument [Line Items]
Amortization of debt issuance fees	6	5
Accretion of debt premium	$ (2)	$ (3)

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Amount of amortization expense attributable to debt issuance costs.

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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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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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