Employee Postretirement Benefits - Schedule of Assumptions Used to Determine Benefit (Detail)	2 Months Ended		6 Months Ended		8 Months Ended	12 Months Ended
	Dec. 31, 2014	Oct. 30, 2014	Dec. 31, 2016	Jun. 30, 2016	Sep. 01, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate			4.11%			4.11%	4.688%
Rate of compensation increase-weighted average			2.57%			2.57%	3.87%
Discount rate	4.331%	4.277%			5.118%	4.688%	4.258%
Expected long-term return on plan assets	7.00%	7.00%			7.25%	7.00%	7.00%
Rate of compensation increase						2.59%	3.87%	3.73%
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate			4.28%			4.28%	4.667%
Rate of compensation increase-weighted average			2.48%			2.48%	2.50%
Healthcare cost trend rate
Immediate rate			6.83%			6.83%	7.05%
Ultimate rate			4.50%			4.50%	4.50%
Year rate reaches ultimate			2038			2038	2038
Other Postretirement Benefits [Member] | Net Periodic Benefit Cost [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate			3.85%	4.667%			4.206%	5.096%
Rate of compensation increase						2.50%	3.86%	3.71%
Healthcare cost trend rate
Immediate rate						7.05%	7.00%	7.25%
Ultimate rate						4.50%	4.50%	4.50%
Year rate reaches ultimate	2025		2038			2038	2025	2025