Pension and Other Postretirement Benefit Plans - Pension Plan Assets by Asset Category (Detail) - Pension - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
U.S.
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	$ 330.6	$ 438.2	$ 412.6
U.S. | Fair value, measurements, recurring
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	330.6	438.2
Assets at fair value, excluding alternative investments	283.1	387.9
U.S. | Fair value, measurements, recurring | Mutual funds/Equity funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	89.1	149.6
U.S. | Fair value, measurements, recurring | Common stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	61.2	80.5
U.S. | Fair value, measurements, recurring | Mutual funds/Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	78.6	101.6
U.S. | Fair value, measurements, recurring | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	47.7	24.8
U.S. | Fair value, measurements, recurring | Government obligations
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	1.0	23.5
U.S. | Fair value, measurements, recurring | Preferred stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	1.3	1.5
U.S. | Fair value, measurements, recurring | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	4.2	6.4
U.S. | Fair value, measurements, recurring | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	187.6	308.7
U.S. | Fair value, measurements, recurring | Level 1 | Mutual funds/Equity funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	74.4	149.6
U.S. | Fair value, measurements, recurring | Level 1 | Common stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	33.6	54.9
U.S. | Fair value, measurements, recurring | Level 1 | Mutual funds/Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	78.6	101.6
U.S. | Fair value, measurements, recurring | Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
U.S. | Fair value, measurements, recurring | Level 1 | Government obligations
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
U.S. | Fair value, measurements, recurring | Level 1 | Preferred stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.8	1.0
U.S. | Fair value, measurements, recurring | Level 1 | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.2	1.6
U.S. | Fair value, measurements, recurring | Level 2
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	95.5	79.2
U.S. | Fair value, measurements, recurring | Level 2 | Mutual funds/Equity funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	14.7	0.0
U.S. | Fair value, measurements, recurring | Level 2 | Common stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	27.6	25.6
U.S. | Fair value, measurements, recurring | Level 2 | Mutual funds/Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
U.S. | Fair value, measurements, recurring | Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	47.7	24.8
U.S. | Fair value, measurements, recurring | Level 2 | Government obligations
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	1.0	23.5
U.S. | Fair value, measurements, recurring | Level 2 | Preferred stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.5	0.5
U.S. | Fair value, measurements, recurring | Level 2 | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	4.0	4.8
U.S. | Fair value, measurements, recurring | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
U.S. | Fair value, measurements, recurring | Level 3 | Mutual funds/Equity funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
U.S. | Fair value, measurements, recurring | Level 3 | Common stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
U.S. | Fair value, measurements, recurring | Level 3 | Mutual funds/Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
U.S. | Fair value, measurements, recurring | Level 3 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
U.S. | Fair value, measurements, recurring | Level 3 | Government obligations
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
U.S. | Fair value, measurements, recurring | Level 3 | Preferred stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
U.S. | Fair value, measurements, recurring | Level 3 | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
U.S. | Fair value, measurements, recurring | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	47.5	50.3
Foreign
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	351.8	406.4	$ 367.1
Foreign | Fair value, measurements, recurring
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	351.8	406.4
Assets at fair value, excluding alternative investments	317.7	370.6
Foreign | Fair value, measurements, recurring | Mutual funds/Equity funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	138.1	163.3
Foreign | Fair value, measurements, recurring | Common stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	58.3	71.6
Foreign | Fair value, measurements, recurring | Mutual funds/Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	28.2	30.9
Foreign | Fair value, measurements, recurring | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	32.9	37.0
Foreign | Fair value, measurements, recurring | Government obligations
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	52.8	58.8
Foreign | Fair value, measurements, recurring | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	7.4	9.0
Foreign | Fair value, measurements, recurring | Level 1
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	62.3	75.0
Foreign | Fair value, measurements, recurring | Level 1 | Mutual funds/Equity funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Level 1 | Common stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	58.3	71.6
Foreign | Fair value, measurements, recurring | Level 1 | Mutual funds/Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Level 1 | Government obligations
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Level 1 | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	4.0	3.4
Foreign | Fair value, measurements, recurring | Level 2
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	255.4	295.6
Foreign | Fair value, measurements, recurring | Level 2 | Mutual funds/Equity funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	138.1	163.3
Foreign | Fair value, measurements, recurring | Level 2 | Common stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Level 2 | Mutual funds/Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	28.2	30.9
Foreign | Fair value, measurements, recurring | Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	32.9	37.0
Foreign | Fair value, measurements, recurring | Level 2 | Government obligations
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	52.8	58.8
Foreign | Fair value, measurements, recurring | Level 2 | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	3.4	5.6
Foreign | Fair value, measurements, recurring | Level 3
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Level 3 | Mutual funds/Equity funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Level 3 | Common stock
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Level 3 | Mutual funds/Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Level 3 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Level 3 | Government obligations
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Level 3 | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	0.0	0.0
Foreign | Fair value, measurements, recurring | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Assets at fair value	$ 34.1	$ 35.8