Long-Term Debt (Revenue Bonds) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 2,715	$ 3,853
Weighted average interest rate on all long-term debt	4.40%	4.50%
Unamortized Debt Issuance Cost	$ 25	$ 26
Long-term Debt, Maturities, Repayments of Principal in Year Five	250
Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 11	$ 11
Debt Instrument, Interest Rate, Effective Percentage	1.85%	1.73%

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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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Weighted average interest rate of long-term debt outstanding calculated at point in time.

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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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