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