Pension Benefits - Changes in Benefit Obligation and Plan Assets (Details) - Pension Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 25, 2016	Dec. 27, 2015
Change in benefit obligation
Benefit obligation at beginning of year	$ 2,039,051	$ 2,098,997
Service cost	9,799	9,134	$ 12,089
Interest cost	68,582	74,465	84,596
Plan participants’ contributions	9	9
Actuarial loss	158,322	26,689
Curtailments	0	(1,599)
Settlements	(269,287)	(48,413)
Benefits paid	(124,838)	(120,124)
Effects of change in currency conversion	152	(107)
Benefit obligation at end of year	1,881,790	2,039,051	2,098,997
Change in plan assets
Fair value of plan assets at beginning of year	1,576,760	1,579,356
Actual return on plan assets	238,622	142,137
Employer contributions	146,145	23,795
Plan participants’ contributions	9	9
Settlements	(269,287)	(48,413)
Benefits paid	(124,838)	(120,124)
Fair value of plan assets at end of year	1,567,411	1,576,760	1,579,356
Amount recognized in the Consolidated Balance Sheets
Current liabilities	(16,901)	(16,818)
Noncurrent liabilities	(297,478)	(445,473)
Net amount recognized	(314,379)	(462,291)
Amount recognized in accumulated other comprehensive loss
Actuarial loss	751,074	863,951
Prior service credit	(20,731)	(22,676)
Total	730,343	841,275
Qualified Plan [Member]
Change in benefit obligation
Benefit obligation at beginning of year	1,798,652	1,851,910
Service cost	9,720	8,991	11,932
Interest cost	60,742	66,293	74,536
Plan participants’ contributions	9	9
Actuarial loss	142,980	23,994
Curtailments	0	0
Settlements	(269,287)	(48,413)
Benefits paid	(106,328)	(104,132)
Effects of change in currency conversion	0	0
Benefit obligation at end of year	1,636,488	1,798,652	1,851,910
Change in plan assets
Fair value of plan assets at beginning of year	1,576,760	1,579,356
Actual return on plan assets	238,622	142,137
Employer contributions	127,635	7,803
Plan participants’ contributions	9	9
Settlements	(269,287)	(48,413)
Benefits paid	(106,328)	(104,132)
Fair value of plan assets at end of year	1,567,411	1,576,760	1,579,356
Amount recognized in the Consolidated Balance Sheets
Current liabilities	0	0
Noncurrent liabilities	(69,077)	(221,892)
Net amount recognized	(69,077)	(221,892)
Amount recognized in accumulated other comprehensive loss
Actuarial loss	641,194	765,096
Prior service credit	(20,731)	(22,676)
Total	620,463	742,420
Nonqualified Plan [Member]
Change in benefit obligation
Benefit obligation at beginning of year	240,399	247,087
Service cost	79	143	157
Interest cost	7,840	8,172	10,060
Plan participants’ contributions	0	0
Actuarial loss	15,342	2,695
Curtailments	0	(1,599)
Settlements	0	0
Benefits paid	(18,510)	(15,992)
Effects of change in currency conversion	152	(107)
Benefit obligation at end of year	245,302	240,399	247,087
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	18,510	15,992
Plan participants’ contributions	0	0
Settlements	0	0
Benefits paid	(18,510)	(15,992)
Fair value of plan assets at end of year	0	0	$ 0
Amount recognized in the Consolidated Balance Sheets
Current liabilities	(16,901)	(16,818)
Noncurrent liabilities	(228,401)	(223,581)
Net amount recognized	(245,302)	(240,399)
Amount recognized in accumulated other comprehensive loss
Actuarial loss	109,880	98,855
Prior service credit	0	0
Total	$ 109,880	$ 98,855