Employee Benefit Plans (Weighted Average Target Pension Plan Asset Allocations) (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Equity Securities
Asset Category
Weighted average target pension plan asset allocation, minimum	15.00%	30.00%
Weighted average target pension plan asset allocation, maximum	45.00%	65.00%
Debt Securities
Asset Category
Weighted average target pension plan asset allocation, minimum	30.00%	30.00%
Weighted average target pension plan asset allocation, maximum	65.00%	65.00%
Real Estate
Asset Category
Weighted average target pension plan asset allocation, minimum	0.00%	0.00%
Weighted average target pension plan asset allocation, maximum	10.00%	10.00%
Other
Asset Category
Weighted average target pension plan asset allocation, minimum	20.00%	0.00%
Weighted average target pension plan asset allocation, maximum	40.00%	20.00%