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

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Fair Value Measurements (Schedule Of Carrying And Fair Values Of Long-Term Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Jul. 17, 2019
Senior Notes [Member] \| 3.60% Senior Notes Due 2022 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 249	$ 249
Stated interest rate (percent)	3.60%
Senior Notes [Member] \| 3.60% Senior Notes Due 2026 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 744	742
Stated interest rate (percent)	3.60%
Senior Notes [Member] \| Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 11	11
Senior Notes [Member] \| 1.625% Senior Notes Due 2029
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 849	774	$ 779
Stated interest rate (percent)	1.625%
Senior Notes [Member] \| 6 1/2% GO Zone Senior Notes Due 2029 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 0	99
Stated interest rate (percent)	6.50%
Senior Notes [Member] \| 3.375 Senior Notes Due 2030
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 296	0
Stated interest rate (percent)	3.375%
Senior Notes [Member] \| 3.50% Senior Notes Due 2032 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 249	249
Stated interest rate (percent)	3.50%
Senior Notes [Member] \| 6 1/2% GO Zone Senior Notes Due 2035 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 0	88
Stated interest rate (percent)	6.50%
Senior Notes [Member] \| 6.5% 2035 IKE Zone Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 0	65
Stated interest rate (percent)	6.50%
Senior Notes [Member] \| 5.0% 2046 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 677	677
Stated interest rate (percent)	5.00%
Senior Notes [Member] \| 4.375% Senior Notes Due 2047 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 491	491
Stated interest rate (percent)	4.375%
Estimate of Fair Value Measurement [Member] \| Senior Notes [Member] \| 3.60% Senior Notes Due 2022 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 259	255
Estimate of Fair Value Measurement [Member] \| Senior Notes [Member] \| 3.60% Senior Notes Due 2026 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	846	777
Estimate of Fair Value Measurement [Member] \| Senior Notes [Member] \| 1.625% Senior Notes Due 2029
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	897	785
Estimate of Fair Value Measurement [Member] \| Senior Notes [Member] \| 6 1/2% GO Zone Senior Notes Due 2029 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0	103
Estimate of Fair Value Measurement [Member] \| Senior Notes [Member] \| 3.375 Senior Notes Due 2030
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	332	0
Estimate of Fair Value Measurement [Member] \| Senior Notes [Member] \| 3.50% Senior Notes Due 2032 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	276	267
Estimate of Fair Value Measurement [Member] \| Senior Notes [Member] \| 6 1/2% GO Zone Senior Notes Due 2035 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0	92
Estimate of Fair Value Measurement [Member] \| Senior Notes [Member] \| 6.5% 2035 IKE Zone Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0	68
Estimate of Fair Value Measurement [Member] \| Senior Notes [Member] \| 5.0% 2046 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	905	761
Estimate of Fair Value Measurement [Member] \| Senior Notes [Member] \| 4.375% Senior Notes Due 2047 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	597	505
Estimate of Fair Value Measurement [Member] \| Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member] \| Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 11	$ 11