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Long-Term Debt (Schedule Of Long-Term Debt) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Jul. 17, 2019	Dec. 31, 2018	Nov. 30, 2017	Aug. 10, 2016	Jul. 31, 2012	Dec. 31, 2010
Debt Instrument [Line Items]
Long-term Debt, Gross Excluding Current Maturities	$ 3,500		$ 2,715
Debt Instrument, Unamortized Premium (Discount) and Debt Issuance Cost, Net, Excluding Current Maturities	(55)		(47)
Long-term Debt, Excluding Current Maturities	$ 3,445		2,668
Senior Notes [Member] \| 3.60% Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument maturity	2022
Stated interest rate (percent)	3.60%
Principal amount	$ 250		250			$ 250
Unamortized Premium (Discount) and Debt Issuance Costs	(1)		(1)
Long-term debt, net	$ 249		249
Senior Notes [Member] \| 3.60% Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt instrument maturity	2026
Stated interest rate (percent)	3.60%
Principal amount	$ 750		750		$ 750
Unamortized Premium (Discount) and Debt Issuance Costs	(8)		(9)
Long-term debt, net	$ 742		741
Senior Notes [Member] \| Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument maturity	2027
Principal amount	$ 11		11
Unamortized Premium (Discount) and Debt Issuance Costs	0		0
Long-term debt, net	$ 11		11
Senior Notes [Member] \| 6 1/2% GO Zone Senior Notes Due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument maturity	2029
Stated interest rate (percent)	6.50%
Principal amount	$ 100		100
Unamortized Premium (Discount) and Debt Issuance Costs	(1)		(1)
Long-term debt, net	$ 99		99
Senior Notes [Member] \| 6 1/2% GO Zone Senior Notes Due 2035 [Member]
Debt Instrument [Line Items]
Debt instrument maturity	2035
Stated interest rate (percent)	6.50%
Principal amount	$ 89		89				$ 89
Unamortized Premium (Discount) and Debt Issuance Costs	(1)		(1)
Long-term debt, net	$ 88		88
Senior Notes [Member] \| 6.5% 2035 IKE Zone Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument maturity	2035
Stated interest rate (percent)	6.50%
Principal amount	$ 65		65				$ 65
Unamortized Premium (Discount) and Debt Issuance Costs	0		0
Long-term debt, net	$ 65		65
Senior Notes [Member] \| 5.0% 2046 [Member]
Debt Instrument [Line Items]
Debt instrument maturity	2046
Stated interest rate (percent)	5.00%
Principal amount	$ 700		700		$ 700
Unamortized Premium (Discount) and Debt Issuance Costs	(23)		(24)
Long-term debt, net	$ 677		676
Senior Notes [Member] \| 4.375% Senior Notes Due 2047 [Member]
Debt Instrument [Line Items]
Debt instrument maturity	2047
Stated interest rate (percent)	4.375%
Principal amount	$ 500		500	$ 500
Unamortized Premium (Discount) and Debt Issuance Costs	(9)		(9)
Long-term debt, net	$ 491		491
Senior Notes [Member] \| 3.50% Senior Notes Due 2032 [Member]
Debt Instrument [Line Items]
Debt instrument maturity	2032
Stated interest rate (percent)	3.50%
Principal amount	$ 250		250
Unamortized Premium (Discount) and Debt Issuance Costs	(1)		(2)
Long-term debt, net	$ 249		248
Senior Notes [Member] \| 1.625% Senior Notes Due 2029
Debt Instrument [Line Items]
Debt instrument maturity	2029
Stated interest rate (percent)	1.625%
Principal amount	$ 785		0
Unamortized Premium (Discount) and Debt Issuance Costs	(11)		0
Long-term debt, net	$ 774	$ 779	$ 0