Benefit Plans - Weighted Average Assumptions Used to Determine Benefit Obligations (Detail)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jun. 30, 2014
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate		3.90%		3.10%
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate		4.00%		3.60%
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.90%	4.00%	3.70%
Expected long term rate of return on plan assets	7.50%	7.50%	7.50%
Pension Benefits [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	3.90%	3.50%	3.50%
Pension Benefits [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	5.50%	5.50%	5.50%
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.70%	3.70%	3.40%
Expected long term rate of return on plan assets	5.30%	5.30%	5.30%