Weighted Average Target Asset Allocations for Plans (Detail) - Pension Plans, Defined Benefit	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Asset Categories
Defined benefit plan target asset allocations	100.00%	100.00%
Equity Securities
Asset Categories
Defined benefit plan target asset allocations	65.00%	63.00%
Fixed Income Securities
Asset Categories
Defined benefit plan target asset allocations	33.00%	35.00%
Cash Equivalents
Asset Categories
Defined benefit plan target asset allocations	2.00%	2.00%