Employee Benefits - Weighted-average assumptions used to determine future benefit obligations (Details)	Dec. 31, 2015	Dec. 31, 2014
U.K. [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.96%	3.70%
Underlying price inflation	1.88%	1.95%
U.K. [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	3.63%	3.35%
U.K. [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	4.13%	4.05%
U.S. [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.69%	3.37%
U.S. [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.43%	4.08%
Other [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	2.43%	2.03%
Rate of compensation increase	2.00%	2.25%
Underlying price inflation	2.00%	2.00%
Other [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.96%	3.91%
Rate of compensation increase	3.50%	3.50%
Underlying price inflation	2.50%	2.50%