Pension Benefits - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended																	12 Months Ended
	Dec. 25, 2016		Sep. 25, 2016	[1]	Jun. 26, 2016	[1]	Mar. 27, 2016	[1]	Dec. 27, 2015	[2]	Sep. 27, 2015	[2]	Jun. 28, 2015	[2]	Mar. 29, 2015		Jun. 29, 2014	Dec. 25, 2016		Dec. 27, 2015		Dec. 28, 2014
Pension Benefits
Decrease in service costs and interest costs																		$ 18,000
Pension settlement charges	$ 21,294	[1]	$ 0		$ 0		$ 0		$ 0		$ 0		$ 0		$ 40,329	[2]		21,294	[1]	$ 40,329	[2]	$ 9,525
Lump-sum payments made from Company cash	49,500														98,300		$ 24,000
Qualified Plans [Member]
Pension Benefits
Service cost																		8,991		11,932		9,543
Interest cost																		66,293		74,536		84,447
Expected return on plan assets																		(111,159)		(115,261)		(113,839)
Amortization and other costs																		28,274		36,442		26,620
Amortization of prior service (credit)/cost																		(1,945)		(1,945)		(1,945)
Effect of settlement/curtailment																		21,294		40,329		0
Net periodic postretirement benefit (income)/expense																		11,748		46,033		4,826
Pension settlement charges																		48,413		98,348
Lump-sum payments to be made from plan assets																		48,413		98,348
Non-Qualified Plans [Member]
Pension Benefits
Service cost																		143		157		184
Interest cost																		8,172		10,060		10,450
Expected return on plan assets																		0		0		0
Amortization and other costs																		4,184		5,081		4,718
Amortization of prior service (credit)/cost																		0		0		0
Effect of settlement/curtailment																		(1,599)		0		9,525
Net periodic postretirement benefit (income)/expense																		10,900		15,298		24,877
Pension settlement charges																		0		0
Lump-sum payments to be made from plan assets																		0		0
Pension Plan [Member]
Pension Benefits
Service cost																		9,134		12,089		9,727
Interest cost																		74,465		84,596		94,897
Expected return on plan assets																		(111,159)		(115,261)		(113,839)
Amortization and other costs																		32,458		41,523		31,338
Amortization of prior service (credit)/cost																		(1,945)		(1,945)		(1,945)
Effect of settlement/curtailment																		19,695		40,329		9,525
Net periodic postretirement benefit (income)/expense																		22,648		61,331		$ 29,703
Pension settlement charges	21,300														40,300		9,500	48,413		98,348
Lump-sum payments to be made from plan assets																		$ 48,413		$ 98,348
Reduction in pension benefit obligation	52,200														$ 142,800		$ 32,000
Curtailment	$ (1,600)

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

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