Long-term Debt and Interest Expense (Components Of Long-Term Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Outstanding debt principal balances, gross	$ 2,300	$ 2,300
Issuance costs and discounts	(11)	(16)
Total debt	2,289	2,284
Less current portion of long-term debt	450	0
Long-term debt	1,839	$ 2,284
7.50% senior notes due 2020
Debt Instrument [Line Items]
Senior notes, interest rate		7.50%
Outstanding debt principal balances, gross	450	$ 450
3.45% senior notes due 2021
Debt Instrument [Line Items]
Senior notes, interest rate		3.45%
Outstanding debt principal balances, gross	500	$ 500
3.95% senior notes due 2022
Debt Instrument [Line Items]
Senior notes, interest rate		3.95%
Outstanding debt principal balances, gross	600	$ 600
4.45% senior notes due 2026
Debt Instrument [Line Items]
Senior notes, interest rate		4.45%
Outstanding debt principal balances, gross	500	$ 500
7.20% senior notes due 2028
Debt Instrument [Line Items]
Senior notes, interest rate		7.20%
Outstanding debt principal balances, gross	$ 250	$ 250

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

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Amount of unamortized debt discount (premium) and debt issuance costs.

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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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