Pension Plans, Other Postretirement Benefits, and Defined-Contribution Plans - Weighted-Average Assumptions for Net Periodic Benefit Cost Table (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.75%	3.50%	4.50%
Long-term rate of return on plan assets	6.75%	7.00%	7.00%
Rates of increase in compensation levels	5.00%	4.50%	4.50%
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.25%	4.00%	4.75%
Rates of increase in compensation levels	5.25%	4.50%	4.50%