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Fair Value Measurements (Summary of Carrying and Fair Values of Long Term Debt) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 3,568	$ 3,566
3.60% Senior Notes Due 2022 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 250	249
Stated interest rate (percent)	3.60%
3.6% Senior Notes Due 2026 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 744	744
Stated interest rate (percent)	3.60%
Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 11	11
1.625% Senior Notes Due 2029 | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 811	849
Stated interest rate (percent)	1.625%
3.375% Senior Notes Due 2030 | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 296	296
Stated interest rate (percent)	3.375%
3.50% Senior Notes Due 2032 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 249	249
Stated interest rate (percent)	3.50%
5.0% Senior Notes Due 2046 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 678	677
Stated interest rate (percent)	5.00%
4.375% Senior Notes Due 2047 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 491	491
Stated interest rate (percent)	4.375%
8.73% Senior Notes Due 2022 | Line of Credit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Stated interest rate (percent)	8.73%
8.73% Senior Notes Due 2022 | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 34	0
Stated interest rate (percent)	8.73%
Term Loan Due Twenty Twenty Six | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 4	0
Stated interest rate (percent)	0.20%
Fair Value [Member] | 3.60% Senior Notes Due 2022 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 257	259
Fair Value [Member] | 3.6% Senior Notes Due 2026 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	809	846
Fair Value [Member] | Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	11	11
Fair Value [Member] | 1.625% Senior Notes Due 2029 | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	855	897
Fair Value [Member] | 3.375% Senior Notes Due 2030 | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	312	332
Fair Value [Member] | 3.50% Senior Notes Due 2032 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	275	276
Fair Value [Member] | 5.0% Senior Notes Due 2046 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	827	905
Fair Value [Member] | 4.375% Senior Notes Due 2047 [Member] | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	544	597
Fair Value [Member] | 8.73% Senior Notes Due 2022 | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	34	0
Fair Value [Member] | Term Loan Due Twenty Twenty Six | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 4	$ 0

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- Definition

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

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