Pension Benefits - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended																	12 Months Ended
	Dec. 27, 2015	[1]	Sep. 27, 2015	[1]	Jun. 28, 2015	[1]	Mar. 29, 2015		Dec. 28, 2014	[2]	Sep. 28, 2014	[2]	Jun. 29, 2014		Mar. 30, 2014	[2]	Dec. 29, 2013	Dec. 27, 2015		Dec. 28, 2014		Dec. 29, 2013
Pension Benefits
Pension settlement charge	$ 0		$ 0		$ 0		$ 40,329	[1]	$ 0		$ 0		$ 9,525	[2]	$ 0			$ 40,329	[1]	$ 9,525	[2]	$ 3,228
Lump-sum payments made from Company cash													24,000				$ 10,900
Qualified Plans [Member]
Pension Benefits
Service cost																		11,932		9,543		11,225
Interest cost																		74,536		84,447		77,136
Expected return on plan assets																		(115,261)		(113,839)		(124,250)
Amortization and other costs																		36,442		26,620		33,770
Amortization of prior service (credit)/cost																		(1,945)		(1,945)		(1,945)
Effect of settlement																		40,329		0		0
Net periodic postretirement benefit (income)/expense																		46,033		4,826		(4,064)
Pension settlement charge																		98,348		0
Lump-sum payments to be made from plan assets																		98,348		0
Non-Qualified Plans [Member]
Pension Benefits
Service cost																		157		184		1,162
Interest cost																		10,060		10,450		10,681
Expected return on plan assets																		0		0		0
Amortization and other costs																		5,081		4,718		5,561
Amortization of prior service (credit)/cost																		0		0		0
Effect of settlement																		0		9,525		3,228
Net periodic postretirement benefit (income)/expense																		15,298		24,877		20,632
Pension settlement charge																		0		24,015
Lump-sum payments to be made from plan assets																		0		24,015
Pension Plan [Member]
Pension Benefits
Service cost																		12,089		9,727		12,387
Interest cost																		84,596		94,897		87,817
Expected return on plan assets																		(115,261)		(113,839)		(124,250)
Amortization and other costs																		41,523		31,338		39,331
Amortization of prior service (credit)/cost																		(1,945)		(1,945)		(1,945)
Effect of settlement																		40,329		9,525		3,228
Net periodic postretirement benefit (income)/expense																		61,331		29,703		$ 16,568
Pension settlement charge							40,300						9,500				3,200	98,348		24,015
Lump-sum payments to be made from plan assets							98,300											$ 98,348		$ 24,015
Reduction in pension benefit obligation							$ 142,800						$ 32,000				$ 12,700

[1] We recorded a settlement charge related to a lump-sum payment offer to certain former employees who participated in a non-qualified pension plan.

[2] We recorded a settlement charge related to a lump-sum payment offer to certain former employees who participated in a non-qualified pension plan.