U.K. Pension Plan Weighted Average Expected Return on Plan Assets (Details) - Pension Plan [Member] - Foreign Plan [Member]	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Weighted Average Expected Return on Plan Assets	6.00%	6.10%	6.10%
Growth, Private equity and infrastructure pooled funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted Average Expected Yields	7.10%	7.10%	6.90%
Weighted Average Asset Allocations	81.00%	82.00%	81.00%
Weighted Average Expected Return on Plan Assets	5.70%	5.80%	5.60%
Defensive and government bond pooled fund plus cash [Member] [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted Average Expected Yields	1.40%	1.50%	2.80%
Weighted Average Asset Allocations	19.00%	18.00%	19.00%
Weighted Average Expected Return on Plan Assets	0.30%	0.30%	0.50%