Retirement Plans - Target allocation ranges (Details) - Pension Benefits	Dec. 30, 2017
United States | Minimum | Domestic Equity Securities
Target allocation ranges
Target plan asset allocations	20.00%
United States | Minimum | International Equity Securities
Target allocation ranges
Target plan asset allocations	8.00%
United States | Minimum | Global equities
Target allocation ranges
Target plan asset allocations	0.00%
United States | Minimum | Debt securities
Target allocation ranges
Target plan asset allocations	27.00%
United States | Minimum | Real estate
Target allocation ranges
Target plan asset allocations	7.00%
United States | Minimum | Private investment partnerships
Target allocation ranges
Target plan asset allocations	5.00%
United States | Minimum | Hedge funds
Target allocation ranges
Target plan asset allocations	0.00%
United States | Maximum | Domestic Equity Securities
Target allocation ranges
Target plan asset allocations	35.00%
United States | Maximum | International Equity Securities
Target allocation ranges
Target plan asset allocations	19.00%
United States | Maximum | Global equities
Target allocation ranges
Target plan asset allocations	12.00%
United States | Maximum | Debt securities
Target allocation ranges
Target plan asset allocations	38.00%
United States | Maximum | Real estate
Target allocation ranges
Target plan asset allocations	13.00%
United States | Maximum | Private investment partnerships
Target allocation ranges
Target plan asset allocations	11.00%
United States | Maximum | Hedge funds
Target allocation ranges
Target plan asset allocations	5.00%
Non-U.S. | Real estate
Target allocation ranges
Target plan asset allocations	8.00%
Non-U.S. | Minimum | Equity securities
Target allocation ranges
Target plan asset allocations	58.00%
Non-U.S. | Minimum | Debt securities
Target allocation ranges
Target plan asset allocations	31.00%
Non-U.S. | Maximum | Equity securities
Target allocation ranges
Target plan asset allocations	61.00%
Non-U.S. | Maximum | Debt securities
Target allocation ranges
Target plan asset allocations	34.00%