Allocation of Plan Assets by Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	$ 2,013.1	$ 1,676.2
Plan assets	2,494.1	2,219.0	$ 2,309.4
Equity Funds | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	$ 1,436.9	$ 1,268.0
Equity Funds
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Equity funds, target minimum	50.00%	50.00%
Equity funds, target maximum	70.00%	70.00%
Plan assets	$ 1,436.9	$ 1,268.0
Equity Funds | United States | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	690.8	593.8
Equity Funds | United States
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	690.8	593.8
Equity Funds | Global | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	746.1	674.2
Equity Funds | Global
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	746.1	674.2
Fixed Income Funds | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	$ 572.3	$ 405.6
Fixed Income Funds
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Equity funds, target minimum	30.00%	30.00%
Equity funds, target maximum	50.00%	50.00%
Plan assets	$ 984.5	$ 885.3
Fixed Income Funds | United States | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	317.8	174.3
Fixed Income Funds | United States
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	710.4	631.6
Fixed Income Funds | Non U.S. | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	254.5	231.3
Fixed Income Funds | Non U.S.
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	274.1	253.7
Cash and other | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	3.9	2.6
Cash and other
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	72.7	65.7
Level 1
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	204.5	291.6
Level 1 | Fixed Income Funds
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	195.7	283.4
Level 1 | Fixed Income Funds | United States
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	195.7	283.4
Level 1 | Cash and other
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	8.8	8.2
Level 2
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	276.5	251.2
Level 2 | Fixed Income Funds
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	216.5	196.3
Level 2 | Fixed Income Funds | United States
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	196.9	173.9
Level 2 | Fixed Income Funds | Non U.S.
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	19.6	22.4
Level 2 | Cash and other
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	60.0	54.9
Fair Value Inputs Level 1 And Level 2 [Member]
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	481.0	542.8
Fair Value Inputs Level 1 And Level 2 [Member] | Fixed Income Funds
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	412.2	479.7
Fair Value Inputs Level 1 And Level 2 [Member] | Fixed Income Funds | United States
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	392.6	457.3
Fair Value Inputs Level 1 And Level 2 [Member] | Fixed Income Funds | Non U.S.
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	19.6	22.4
Fair Value Inputs Level 1 And Level 2 [Member] | Cash and other
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	$ 68.8	$ 63.1