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Debt - Schedule of Debt (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SHORT-TERM DEBT
Short-term debt	$ 66,000,000	$ 737,000,000
LONG-TERM DEBT
Senior notes, net of unamortized discounts and debt issuance costs	8,941,000,000	8,933,000,000
Noncurrent portion of other long-term debt	202,000,000	250,000,000
Total long-term debt	9,143,000,000	9,183,000,000
Total debt	9,209,000,000	9,920,000,000
Other
SHORT-TERM DEBT
Short-term debt	66,000,000	73,000,000
Senior secured hedged inventory facility \| Line of Credit
SHORT-TERM DEBT
Short-term notes and borrowings	0	$ 664,000,000
Weighted average interest rate, short-term (as a percent)		2.60%
Senior notes
LONG-TERM DEBT
Unamortized discounts and debt issuance costs	(59,000,000)	$ (67,000,000)
Senior notes, net of unamortized discounts and debt issuance costs	8,941,000,000	8,933,000,000
Debt instrument face value	9,000,000,000	9,000,000,000
Senior notes \| Level 2
LONG-TERM DEBT
Debt instrument fair value	8,600,000,000	9,100,000,000
Senior notes \| 2.60% senior notes due December 2019 (2)
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 500,000,000	500,000,000
Debt instrument, interest rate (as a percent)	2.60%
Debt instrument face value	$ 500,000,000
Senior notes \| 5.75% senior notes due January 2020
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 500,000,000	500,000,000
Debt instrument, interest rate (as a percent)	5.75%
Senior notes \| 5.00% senior notes due February 2021
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 600,000,000	600,000,000
Debt instrument, interest rate (as a percent)	5.00%
Senior notes \| 3.65% senior notes due June 2022
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 750,000,000	750,000,000
Debt instrument, interest rate (as a percent)	3.65%
Senior notes \| 2.85% senior notes due January 2023
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 400,000,000	400,000,000
Debt instrument, interest rate (as a percent)	2.85%
Senior notes \| 3.85% senior notes due October 2023
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 700,000,000	700,000,000
Debt instrument, interest rate (as a percent)	3.85%
Senior notes \| 3.60% senior notes due November 2024
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 750,000,000	750,000,000
Debt instrument, interest rate (as a percent)	3.60%
Senior notes \| 4.65% senior notes due October 2025
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 1,000,000,000	1,000,000,000
Debt instrument, interest rate (as a percent)	4.65%
Senior notes \| 4.50% senior notes due December 2026
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 750,000,000	750,000,000
Debt instrument, interest rate (as a percent)	4.50%		4.50%
Debt instrument face value			$ 750,000,000
Senior notes \| 6.70% senior notes due May 2036
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 250,000,000	250,000,000
Debt instrument, interest rate (as a percent)	6.70%
Senior notes \| 6.65% senior notes due January 2037
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 600,000,000	600,000,000
Debt instrument, interest rate (as a percent)	6.65%
Senior notes \| 5.15% senior notes due June 2042
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 500,000,000	500,000,000
Debt instrument, interest rate (as a percent)	5.15%
Senior notes \| 4.30% senior notes due January 2043
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 350,000,000	350,000,000
Debt instrument, interest rate (as a percent)	4.30%
Senior notes \| 4.70% senior notes due June 2044
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 700,000,000	700,000,000
Debt instrument, interest rate (as a percent)	4.70%
Senior notes \| 4.90% senior notes due February 2045
LONG-TERM DEBT
Long-term debt, before deducting unamortized discounts and debt issuance costs	$ 650,000,000	650,000,000
Debt instrument, interest rate (as a percent)	4.90%
Commercial Paper \| Senior secured hedged inventory facility
LONG-TERM DEBT
Noncurrent portion of other long-term debt		$ 247,000,000
Weighted average long term debt interest rate		2.40%
Term Loan \| GO Zone Term Loans
LONG-TERM DEBT
Noncurrent portion of other long-term debt	$ 198,000,000
Debt issuance costs	$ 2,000,000
Weighted average long term debt interest rate	3.10%
Other
LONG-TERM DEBT
Noncurrent portion of other long-term debt	$ 4,000,000	$ 3,000,000