Postretirement Benefit Plans (Assumptions used to determine the benefit obligation and net periodic benefit cost) (Details) - Korea Defined Benefit Plan	Dec. 31, 2018	Dec. 31, 2017
Weighted-average assumptions used to determine benefit obligation and net periodic defined benefit plan cost:
Discount rate	2.46%	2.98%
Rate of compensation increase	6.96%	6.11%

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Period Type:	instant