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, 2016	Dec. 31, 2015
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	45.90%	38.00%
Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of managed fund	15.00%
Fixed Income Securities [Member] | Managed Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of managed fund	7.40%
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	44.50%	43.00%
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		19.00%
Other, Primarily 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	2.20%