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Employee Benefits - Expected Long Term Rates of Return on Different Asset Classes (Details) - United Kingdom	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	2.00%	2.10%	3.00%
Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	2.90%
Gilts
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	1.80%
Cash
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	2.90%

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- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit 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 (k)(3)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

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+ References

No definition available.

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