Pension Benefits - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 29, 2019	Dec. 30, 2018	Dec. 31, 2017
Pension Benefits
Pension settlement expense		$ 0	$ 0	$ 102,109
Pension Plan
Pension Benefits
Service cost		5,231	10,065	9,799
Interest cost		67,255	60,153	68,582
Expected return on plan assets		(80,877)	(82,327)	(102,900)
Amortization and other costs		23,020	31,916	33,369
Amortization of prior service (credit)/cost		(1,932)	(1,945)	(1,945)
Effect of settlement/curtailment		(373)	221	102,109
Net periodic pension (income)/cost		12,324	18,083	109,014
Reduction in pension benefit obligation	$ 263,300
Pension settlement expense	102,100
Discretionary contributions to pension plans	$ 120,000
Qualified Plan | Pension Plan
Pension Benefits
Service cost		5,113	9,986	9,720
Interest cost		58,835	52,770	60,742
Expected return on plan assets		(80,877)	(82,327)	(102,900)
Amortization and other costs		18,639	26,802	29,051
Amortization of prior service (credit)/cost		(1,945)	(1,945)	(1,945)
Effect of settlement/curtailment		0	0	102,109
Net periodic pension (income)/cost		(235)	5,286	96,777
Pension contributions		9,500
Nonqualified Plan | Pension Plan
Pension Benefits
Service cost		118	79	79
Interest cost		8,420	7,383	7,840
Expected return on plan assets		0	0	0
Amortization and other costs		4,381	5,114	4,318
Amortization of prior service (credit)/cost		13	0	0
Effect of settlement/curtailment		(373)	221	0
Net periodic pension (income)/cost		$ 12,559	$ 12,797	$ 12,237