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Derivatives and Risk Management - Hedge Position (Details) € in Millions, ₩ in Millions, gal in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020 KRW (₩) gal	Dec. 31, 2019 KRW (₩) gal	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 EUR (€)	Nov. 30, 2019 KRW (₩)
Derivatives, Fair Value [Line Items]
Total derivative contracts, net			$ 1	$ 68
Prepaid Expenses and Other
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			3	38
Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			20	53
Other Accrued Liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			(9)	(19)
Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			(13)	(4)
Foreign exchange contract - euro based \| Not designated as hedges
Derivatives, Fair Value [Line Items]
Volume \| €					€ 397
Total derivative contracts, net				9
Foreign exchange contract - euro based \| Not designated as hedges \| Prepaid Expenses and Other
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets				9
Foreign exchange contract - euro based \| Not designated as hedges \| Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets				0
Foreign exchange contract - euro based \| Not designated as hedges \| Other Accrued Liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities				0
Foreign exchange contract - euro based \| Not designated as hedges \| Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities				0
Foreign exchange contract - won based \| Not designated as hedges
Derivatives, Fair Value [Line Items]
Volume \| ₩	₩ 177,045	₩ 177,045				₩ 177,000
Total derivative contracts, net			(13)	(3)
Foreign exchange contract - won based \| Not designated as hedges \| Prepaid Expenses and Other
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			0	1
Foreign exchange contract - won based \| Not designated as hedges \| Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			0	0
Foreign exchange contract - won based \| Not designated as hedges \| Other Accrued Liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			0	0
Foreign exchange contract - won based \| Not designated as hedges \| Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			(13)	(4)
Fuel hedge contracts \| Not designated as hedges
Derivatives, Fair Value [Line Items]
Volume, nonmonetary \| gal	157	243
Total derivative contracts, net			(9)	1
Fuel hedge contracts \| Not designated as hedges \| Prepaid Expenses and Other
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			0	16
Fuel hedge contracts \| Not designated as hedges \| Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			0	0
Fuel hedge contracts \| Not designated as hedges \| Other Accrued Liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			(9)	(15)
Fuel hedge contracts \| Not designated as hedges \| Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			0	0
Fair value hedge \| Interest rate contracts \| Designated as hedges
Derivatives, Fair Value [Line Items]
Volume			150	1,872
Total derivative contracts, net			23	61
Fair value hedge \| Interest rate contracts \| Designated as hedges \| Prepaid Expenses and Other
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			3	12
Fair value hedge \| Interest rate contracts \| Designated as hedges \| Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			20	53
Fair value hedge \| Interest rate contracts \| Designated as hedges \| Other Accrued Liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			0	(4)
Fair value hedge \| Interest rate contracts \| Designated as hedges \| Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			$ 0	$ 0