Benefit Plans - Target Allocation of Assets and Acceptable Ranges (Detail)	12 Months Ended
	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	100.00%
Domestic equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	44.00%
Target allocation of assets, range minimum	35.00%
Target allocation of assets, range maximum	55.00%
Foreign equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	14.00%
Target allocation of assets, range minimum	5.00%
Target allocation of assets, range maximum	25.00%
Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	40.00%
Target allocation of assets, range minimum	30.00%
Target allocation of assets, range maximum	50.00%
Real estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	2.00%
Target allocation of assets, range minimum	0.00%
Target allocation of assets, range maximum	10.00%
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation of assets	0.00%
Target allocation of assets, range minimum	0.00%
Target allocation of assets, range maximum	35.00%