Schedule of Fair Value of Assets and Liabilities (Parenthetical) (Detail) - Recourse Debt	12 Months Ended
	Dec. 29, 2018	Dec. 30, 2017
American & Foreign Power Company, Inc. 5% debentures, due 2030
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate on senior notes	5.00%	5.00%
Carrying Amount | Term Loan, due 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, due date	2022	2022
Carrying Amount | Revenue bonds, due in varying amounts periodically through 2029
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, due date	2029	2029
Carrying Amount | American & Foreign Power Company, Inc. 5% debentures, due 2030
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, due date	2030	2030
Interest rate on senior notes	5.00%	5.00%
Fair Value | Term Loan, due 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, due date	2022	2022
Fair Value | Revenue bonds, due in varying amounts periodically through 2029
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, due date	2029	2029
Fair Value | American & Foreign Power Company, Inc. 5% debentures, due 2030
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, due date	2030	2030
Interest rate on senior notes	5.00%	5.00%