Financial Instruments - Derivatives (Details) € in Millions, ₩ in Millions, ¥ in Millions, ¥ in Millions, £ in Millions, kr in Millions, $ in Millions, $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019 KRW (₩) t	Dec. 31, 2018 KRW (₩) t	Jun. 30, 2019 USD ($)	Jun. 30, 2019 JPY (¥)	Jun. 30, 2019 MXN ($)	Jun. 30, 2019 CNY (¥)	Jun. 30, 2019 SEK (kr)	Jun. 30, 2019 EUR (€)	Jun. 30, 2019 GBP (£)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 JPY (¥)	Dec. 31, 2018 MXN ($)	Dec. 31, 2018 CNY (¥)	Dec. 31, 2018 SEK (kr)	Dec. 31, 2018 EUR (€)	Dec. 31, 2018 GBP (£)
Commodity contracts | Maturity December 2019
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass | t	120	257
Brazil, Brazil Real | Foreign currency | Maturity December 2019
Derivative [Line Items]
Notional amount of currency derivatives			$ 0							$ 5
Brazil, Brazil Real | Foreign currency | Maturity January 2020
Derivative [Line Items]
Notional amount of currency derivatives | €								€ 4							€ 4
United Kingdom, Pounds | Foreign currency | Maturity March 2020
Derivative [Line Items]
Notional amount of currency derivatives			9					23		0					0
China, Yuan Renminbi | Foreign currency | Maturity December 2019
Derivative [Line Items]
Notional amount of currency derivatives			16							0
Euro Member Countries, Euro | Cross Currency Interest Rate Contract [Member] | Maturity September 2020
Derivative [Line Items]
Notional amount of currency derivatives | €								206
Euro Member Countries, Euro | Foreign currency | Maturity December 2019
Derivative [Line Items]
Notional amount of currency derivatives			7	¥ 257		¥ 22			£ 9	19	¥ 0		¥ 0			£ 7
Euro Member Countries, Euro | Foreign currency | Maturity June 2020
Derivative [Line Items]
Notional amount of currency derivatives | kr							kr 540							kr 540
Japan, Yen | Cross Currency Interest Rate Contract [Member] | Maturity February 2023
Derivative [Line Items]
Notional amount of currency derivatives | ¥				10,978
Japan, Yen | Foreign currency | Maturity December 2019
Derivative [Line Items]
Notional amount of currency derivatives	₩ 2,773	₩ 5,785	1			¥ 44				3			¥ 89
Korea (South), Won | Foreign currency | Maturity December 2019
Derivative [Line Items]
Notional amount of currency derivatives			22	¥ 112				3		$ 7	¥ 266				6
Sweden, Kronor | Foreign currency | Maturity January 2020
Derivative [Line Items]
Notional amount of currency derivatives | €								30							56
United States of America, Dollars | Cross Currency Interest Rate Contract [Member] | Maturity September 2020
Derivative [Line Items]
Notional amount of currency derivatives			250
United States of America, Dollars | Cross Currency Interest Rate Contract [Member] | Maturity February 2023
Derivative [Line Items]
Notional amount of currency derivatives			$ 100
United States of America, Dollars | Foreign currency | Maturity December 2019
Derivative [Line Items]
Notional amount of currency derivatives					$ 297							$ 575
United States of America, Dollars | Foreign currency | Maturity January 2020
Derivative [Line Items]
Notional amount of currency derivatives | €								€ 9							€ 0