Postretirement Benefit Plans - Weighted Average Allocations (Details)	Dec. 31, 2017	Dec. 31, 2016
U.S. \| Fixed income securities and cash equivalents \| Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Targeted allocation (in percent)	65.00%
Actual plan asset allocation (in percent)	66.00%	66.00%
U.S. \| Fixed income securities and cash equivalents \| Retiree health care plan
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocation (in percent)	62.00%	52.00%
U.S. \| Fixed income securities and cash equivalents \| Retiree health care plan \| Minimum
Defined Benefit Plan Disclosure [Line Items]
Targeted allocation (in percent)	55.00%
U.S. \| Fixed income securities and cash equivalents \| Retiree health care plan \| Maximum
Defined Benefit Plan Disclosure [Line Items]
Targeted allocation (in percent)	65.00%
U.S. \| Equity securities \| Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Targeted allocation (in percent)	35.00%
Actual plan asset allocation (in percent)	34.00%	34.00%
U.S. \| Equity securities \| Retiree health care plan
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocation (in percent)	38.00%	48.00%
U.S. \| Equity securities \| Retiree health care plan \| Minimum
Defined Benefit Plan Disclosure [Line Items]
Targeted allocation (in percent)	35.00%
U.S. \| Equity securities \| Retiree health care plan \| Maximum
Defined Benefit Plan Disclosure [Line Items]
Targeted allocation (in percent)	45.00%
Non-U.S. \| Fixed income securities and cash equivalents \| Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocation (in percent)	71.00%	72.00%
Non-U.S. \| Fixed income securities and cash equivalents \| Defined benefit plan \| Minimum
Defined Benefit Plan Disclosure [Line Items]
Targeted allocation (in percent)	60.00%
Non-U.S. \| Fixed income securities and cash equivalents \| Defined benefit plan \| Maximum
Defined Benefit Plan Disclosure [Line Items]
Targeted allocation (in percent)	100.00%
Non-U.S. \| Equity securities \| Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocation (in percent)	29.00%	28.00%
Non-U.S. \| Equity securities \| Defined benefit plan \| Minimum
Defined Benefit Plan Disclosure [Line Items]
Targeted allocation (in percent)	0.00%
Non-U.S. \| Equity securities \| Defined benefit plan \| Maximum
Defined Benefit Plan Disclosure [Line Items]
Targeted allocation (in percent)	40.00%

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- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920

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

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