Pensions and Post-Retirement Benefit Plans - Schedule of Pension Plan Assets at Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 188.8	$ 200.9
Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	63.0	62.9
Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	114.0	128.0
Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	11.8	10.0
U.S. equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	31.3	25.5
U.S. equity securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	18.6	12.3
U.S. equity securities [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	12.7	13.2
U.S. equity securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
International equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	25.2	23.5
International equity securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	15.0	12.6
International equity securities [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	10.2	10.9
International equity securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
U.S. debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	76.9	108.1
U.S. debt securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	21.4	29.7
U.S. debt securities [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	53.0	75.2
U.S. debt securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	2.5	3.2
International debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	43.3	33.7
International debt securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	7.5	8.3
International debt securities [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	34.8	24.3
International debt securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.0	1.1
Real estate and other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	9.6	6.2
Real estate and other investments [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.5	0.0
Real estate and other investments [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.8	0.5
Real estate and other investments [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	8.3	5.7
Cash & Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	2.5	3.9
Cash & Cash Equivalents [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Cash & Cash Equivalents [Member] | Significant observable inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	2.5	3.9
Cash & Cash Equivalents [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 0.0	$ 0.0