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	12 Months Ended
	Dec. 31, 2019	Jul. 17, 2019	Dec. 31, 2018
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
Debt instrument maturity	2022
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	$ 742		741
Debt instrument maturity	2026
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
Debt instrument maturity	2027
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	$ 99		99
Debt instrument maturity	2029
Stated interest rate (percent)	6.50%
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	$ 88		88
Debt instrument maturity	2035
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	$ 65		65
Debt instrument maturity	2035
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		676
Debt instrument maturity	2046
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
Debt instrument maturity	2047
Stated interest rate (percent)	4.375%
Senior Notes [Member] \| 3.50% Senior Notes Due 2032 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 249		248
Debt instrument maturity	2032
Stated interest rate (percent)	3.50%
Senior Notes [Member] \| 1.625% Senior Notes Due 2029
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 774	$ 779	0
Debt instrument maturity	2029
Stated interest rate (percent)	1.625%
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	$ 255		248
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	777		692
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	103		106
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	92		95
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	68		69
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	761		641
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	505		417
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	267		233
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	785		0
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