EMPLOYEE BENEFITS - Fair value (Details) (Pension plan, USD $) In Thousands, unless otherwise specified	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
EMPLOYEE BENEFITS
Total	$ 1,478,686	$ 1,426,678
Pending trades		6,017
Fair value of plan assets	1,478,686	1,432,695	1,358,877
Cash and cash equivalents
EMPLOYEE BENEFITS
Total	1,068	844
Mutual funds
EMPLOYEE BENEFITS
Total	485,488	273,450
Corporate debt instruments
EMPLOYEE BENEFITS
Total	106	105
U.S. Government securities
EMPLOYEE BENEFITS
Total		112,530
Common collective trust
EMPLOYEE BENEFITS
Total	937,809	980,317
Real Estate
EMPLOYEE BENEFITS
Total	47,579	52,265
Other
EMPLOYEE BENEFITS
Total	6,636	7,167
Level 1
EMPLOYEE BENEFITS
Total	486,556	274,294
Level 1 | Cash and cash equivalents
EMPLOYEE BENEFITS
Total	1,068	844
Level 1 | Mutual funds
EMPLOYEE BENEFITS
Total	485,488	273,450
Level 2
EMPLOYEE BENEFITS
Total	937,915	1,092,952
Level 2 | Corporate debt instruments
EMPLOYEE BENEFITS
Total	106	105
Level 2 | U.S. Government securities
EMPLOYEE BENEFITS
Total		112,530
Level 2 | Common collective trust
EMPLOYEE BENEFITS
Total	937,809	980,317
Level 3
EMPLOYEE BENEFITS
Total	54,215	59,432	57,987
Level 3 | Real Estate
EMPLOYEE BENEFITS
Total	47,579	52,265
Level 3 | Other
EMPLOYEE BENEFITS
Total	$ 6,636	$ 7,167