Fair Value Measurements (Summary of Carrying and Fair Values of Long Term Debt) (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 3,681	$ 3,445
3.60% Senior Notes Due 2022 [Member] \| Senior Notes [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%
3.6% Senior Notes Due 2026 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 743	742
Debt Instrument Maturity	2026
Stated interest rate (percent)	3.60%
Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 11	11
Debt Instrument Maturity	2027
1.625% Senior Notes Due 2029 \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 811	774
Debt Instrument Maturity	2029
Stated interest rate (percent)	1.625%
6 1/2% GO Zone Senior Notes Due 2029 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 0	99
Debt Instrument Maturity	2029
Stated interest rate (percent)	6.50%
3.375% Senior Notes Due 2030 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 296	0
Debt Instrument Maturity	2030
Stated interest rate (percent)	3.375%
3.50% Senior Notes Due 2032 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 249	249
Debt Instrument Maturity	2032
Stated interest rate (percent)	3.50%
2035 GO Zone 6 1/2% Notes [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 89	88
Debt Instrument Maturity	2035
Stated interest rate (percent)	6.50%
2035 IKE Zone 6 1/2% Notes [Member] \| 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%
5.0% Senior Notes Due 2046 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 677	677
Debt Instrument Maturity	2046
Stated interest rate (percent)	5.00%
4.375% Senior Notes Due 2047 [Member] \| Senior Notes [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%
Fair Value [Member] \| 3.60% Senior Notes Due 2022 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 261	255
Fair Value [Member] \| 3.6% Senior Notes Due 2026 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	826	777
Fair Value [Member] \| Loan related to tax-exempt waste disposal revenue bonds due 2027 [Member] \| Senior Notes [Member]
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 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	809	785
Fair Value [Member] \| 6 1/2% GO Zone Senior Notes Due 2029 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	103
Fair Value [Member] \| 3.375% Senior Notes Due 2030 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	321	0
Fair Value [Member] \| 3.50% Senior Notes Due 2032 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	261	267
Fair Value [Member] \| 2035 GO Zone 6 1/2% Notes [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	89	92
Fair Value [Member] \| 2035 IKE Zone 6 1/2% Notes [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	65	68
Fair Value [Member] \| 5.0% Senior Notes Due 2046 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	809	761
Fair Value [Member] \| 4.375% Senior Notes Due 2047 [Member] \| Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 533	$ 505

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

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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