Employee Benefits - Weighted-average assumptions used to determine the net periodic benefit cost (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
U.K. [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.55%	4.45%	4.80%
Expected return on plan assets	6.00%	6.30%	6.30%
Rate of compensation increase			3.55%
U.K. [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	3.70%	3.25%
U.K. [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	4.40%	3.85%
U.S. [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets	8.80%	8.80%	8.80%
U.S. [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.97%	3.73%	4.33%
U.S. [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.87%	4.05%	4.60%
Other [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.60%	3.25%	4.40%
Expected return on plan assets	4.70%	4.60%	4.90%
Rate of compensation increase	2.25%	2.25%	2.25%
Other [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.71%	3.89%	4.94%
Expected return on plan assets	6.50%	6.50%	6.75%
Rate of compensation increase	3.50%	3.50%	3.50%