Schedule of Fair Value of Senior Notes (Parenthetical) (Detail) - Recourse Debt	6 Months Ended	12 Months Ended
	Jun. 25, 2016	Dec. 26, 2015
9.75% senior secured notes, due 2019 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, interest rate	9.75%	9.75%
Long-term debt, due date	2019	2019
9.75% senior secured notes, due 2019 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, interest rate	9.75%	9.75%
Long-term debt, due date	2019	2019
7.35% debentures, due 2016 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, interest rate	7.35%	7.35%
Long-term debt, due date	2016	2016
7.35% debentures, due 2016 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, interest rate	7.35%	7.35%
Long-term debt, due date	2016	2016
Revenue bonds, due in varying amounts periodically through 2029 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, due date	2029	2029
Revenue bonds, due in varying amounts periodically through 2029 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, due date	2029	2029
American & Foreign Power Company, Inc. 5% debentures, due 2030 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, interest rate	5.00%	5.00%
Long-term debt, due date	2030	2030
American & Foreign Power Company, Inc. 5% debentures, due 2030 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, interest rate	5.00%	5.00%
Long-term debt, due date	2030	2030