Pension and Post-employment Benefits - Reconciliation of Fair Value of Plan Assets Measured Using Significant Unobservable Inputs (Detail) - United Kingdom Plan [Member] - Non-financial Assets and Liabilities (Level 3 Measurement) [Member] - Other Assets [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 152.9	$ 171.9
Realized/unrealized gains/(losses):
Relating to assets still held at the reporting date	2.8	16.8
Relating to assets sold during the period	0.0	0.0
Purchases, issuances and settlements	(7.4)	(6.7)
Exchange effect	14.5	(29.1)
Ending balance	$ 162.8	$ 152.9

Pension and Post-employment Benefits - Reconciliation of Fair Value of Plan Assets Measured Using Significant Unobservable Inputs (Detail) - United Kingdom Plan [Member] - Non-financial Assets and Liabilities (Level 3 Measurement) [Member] - Other Assets [Member] - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]

Beginning balance

$ 152.9

$ 171.9

Realized/unrealized gains/(losses):

Relating to assets still held at the reporting date

2.8

16.8

Relating to assets sold during the period