Postretirement Benefit Plans - Fair Value of Plan Assets Held by Our Postretirement Benefits Plans (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	$ 283.4	$ 278.0	$ 257.0
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	273.9	268.8
Pension [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	97.6	98.2
Pension [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	53.0	56.6
Pension [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	24.9	25.5
Pension [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	97.1	85.0
Pension [Member] | Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1.3	3.5
Pension [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	273.9	268.8
Pension [Member] | Level 2 [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	97.6	98.2
Pension [Member] | Level 2 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	53.0	56.6
Pension [Member] | Level 2 [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	24.9	25.5
Pension [Member] | Level 2 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	97.1	85.0
Pension [Member] | Level 2 [Member] | Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1.3	3.5
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	9.5	9.2	7.9
Other Postretirement Benefit Plan [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	2.8	0
Other Postretirement Benefit Plan [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1.9	0
Other Postretirement Benefit Plan [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.9	0
Other Postretirement Benefit Plan [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	2.8	9.2
Other Postretirement Benefit Plan [Member] | Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1.1	0
Other Postretirement Benefit Plan [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	9.5
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	2.8
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1.9
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	0.9
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	2.8
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset	1.1
Other Postretirement Benefit Plan [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		9.2
Other Postretirement Benefit Plan [Member] | Level 3 [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0
Other Postretirement Benefit Plan [Member] | Level 3 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0
Other Postretirement Benefit Plan [Member] | Level 3 [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		0
Other Postretirement Benefit Plan [Member] | Level 3 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		9.2
Other Postretirement Benefit Plan [Member] | Level 3 [Member] | Cash and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan asset		$ 0