Pension and Other Postretirement Benefits - Asset Categories Based on the Nature and Risks of the Plan Assets (Parenthetical) (Detail) (U.S. Pension Benefits [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of managed fund	65.00%
Equity Securities [Member] | Managed Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of managed fund	43.00%	43.00%
Alternative Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of managed fund	15.00%
Alternative Investments [Member] | Managed Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of managed fund	50.00%	50.00%
Fixed Income and Cash and Cash Equivalents [Member] | Managed Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of managed fund	7.00%	7.00%