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Long-Term Debt, Excluding Maturities, Gross

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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The average effective interest rate during the reporting period.

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Contractual interest rate for funds borrowed, under the debt agreement.

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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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Amount, after accumulated amortization, of debt discount (premium).

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

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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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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Debt (Components of Debt) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Debt (Components of Debt) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Sep. 02, 2021	Sep. 01, 2021	Aug. 30, 2021	Aug. 31, 2020	Jun. 30, 2020	Apr. 07, 2020	Jul. 31, 2018	Jan. 31, 2015
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross		$ 3,171
Total debt instrument, gross	$ 4,245
Unamortized Issuance Expense	(34)	(20)
Unamortized debt premium (discount)	26	(1)
Current portion of long-term debt	201	0
Total long-term debt	4,036	3,150
Total debt	4,237
Long-term debt
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross	4,044
Unamortized Issuance Expense	(34)
Unamortized debt premium (discount)	26
Total long-term debt	4,036
Senior Notes
Debt Instrument [Line Items]
Debt Instrument, current portion of long-term debt	201
Unamortized Issuance Expense	0
Unamortized debt premium (discount)	0
Current portion of long-term debt	201
Senior Notes \| 4.10% Senior Notes due March 2022
Debt Instrument [Line Items]
Debt Instrument, current portion of long-term debt	201
Long-term debt, excluding maturity, gross		207
Unamortized Issuance Expense	0	0
Unamortized debt premium (discount)	0	0
Current portion of long-term debt	$ 201
Total long-term debt		$ 207
Stated interest rate	4.10%	4.10%			4.10%		4.10%
Senior Notes \| 4.95% Senior Notes due January 2025
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross	$ 689	$ 856
Unamortized Issuance Expense	(3)	(4)
Unamortized debt premium (discount)	0	(1)
Total long-term debt	$ 686	$ 851
Stated interest rate	4.95%	4.95%		6.20%	4.95%		4.95%	6.45%	6.20%	4.95%
Senior Notes \| 7.50% Senior Notes due April 2026
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross		$ 618
Unamortized Issuance Expense		(6)
Unamortized debt premium (discount)		0
Total long-term debt		$ 612
Stated interest rate		7.50%			7.50%		7.50%
Senior Notes \| 7.75% Senior Notes due October 2027
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross	$ 440	$ 440
Unamortized Issuance Expense	(4)	(5)
Unamortized debt premium (discount)	0	0
Total long-term debt	$ 436	$ 435
Stated interest rate	7.75%	7.75%					7.75%
Senior Notes \| 8.375% Senior Notes due September 2028
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross	$ 350	$ 350
Unamortized Issuance Expense	(5)	(5)
Unamortized debt premium (discount)	0	0
Total long-term debt	$ 345	$ 345
Stated interest rate	8.375%	8.375%				8.375%
Senior Notes \| 5.375% Senior Notes due February 2029
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross	$ 700
Unamortized Issuance Expense	(5)
Unamortized debt premium (discount)	26
Total long-term debt	$ 721
Total debt			$ 700	$ 700
Stated interest rate	5.375%		5.375%	5.375%
Senior Notes \| 5.375% Senior Notes due September 2030
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross	$ 1,200
Unamortized Issuance Expense	(17)
Unamortized debt premium (discount)	0
Total long-term debt	$ 1,183
Stated interest rate	5.375%				5.375%
Line of Credit \| Variable rate (2.08% at September 30, 2021) 2018 revolving credit facility due April 2024
Debt Instrument [Line Items]
Variable interest rate	2.08%
Line of Credit \| Variable rate (2.08% at September 30, 2021) 2018 revolving credit facility due April 2024 \| Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross	$ 665
Unamortized Issuance Expense	0
Unamortized debt premium (discount)	0
Total long-term debt	665
Line of Credit \| Variable rate (2.11% at December 31, 2020) 2018 revolving credit facility due April 2024
Debt Instrument [Line Items]
Long-term debt, excluding maturity, gross		$ 700
Unamortized Issuance Expense		0
Unamortized debt premium (discount)		0
Total long-term debt		$ 700
Variable interest rate		2.11%
Other long-term assets \| Line of Credit \| Variable rate (2.08% at September 30, 2021) 2018 revolving credit facility due April 2024
Debt Instrument [Line Items]
Unamortized Issuance Expense	$ (10)	$ (12)