Postretirement Benefit Plans - Fair Value of Plan Assets Held by Our Postretirement Benefits Plans (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	$ 269.2	$ 286.9	$ 283.4
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	263.1	279.0
Pension [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	67.4	85.8
Pension [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	58.9	65.2
Pension [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	135.0	121.1
Pension [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		4.0
Pension [Member] | Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Pension [Member] | Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1.8	2.9
Pension [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1.8	2.9
Pension [Member] | Level 1 [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Pension [Member] | Level 1 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Pension [Member] | Level 1 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Pension [Member] | Level 1 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0.0
Pension [Member] | Level 1 [Member] | Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Pension [Member] | Level 1 [Member] | Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1.8	2.9
Pension [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		4.0
Pension [Member] | Level 3 [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0.0
Pension [Member] | Level 3 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0.0
Pension [Member] | Level 3 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0.0
Pension [Member] | Level 3 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		4.0
Pension [Member] | Level 3 [Member] | Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0.0
Pension [Member] | Level 3 [Member] | Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0.0
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	6.1	7.9	$ 9.5
Other Postretirement Benefit Plan [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Other Postretirement Benefit Plan [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Other Postretirement Benefit Plan [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Other Postretirement Benefit Plan [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0.0
Other Postretirement Benefit Plan [Member] | Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	6.1	7.9
Other Postretirement Benefit Plan [Member] | Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Other Postretirement Benefit Plan [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	6.1	7.9
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0.0
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	6.1	7.9
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Postretirement Assets Measured at Net Asset Value [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	261.3	272.1
Postretirement Assets Measured at Net Asset Value [Member] | Pension [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	67.4	85.8
Postretirement Assets Measured at Net Asset Value [Member] | Pension [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	58.9	65.2
Postretirement Assets Measured at Net Asset Value [Member] | Pension [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	135.0	121.1
Postretirement Assets Measured at Net Asset Value [Member] | Pension [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0.0
Postretirement Assets Measured at Net Asset Value [Member] | Pension [Member] | Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.0	0.0
Postretirement Assets Measured at Net Asset Value [Member] | Pension [Member] | Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	$ 0.0	$ 0.0