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Investment in Unconsolidated Affiliates (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Jan. 03, 2015
stores
Dec. 28, 2013
Dec. 29, 2012
Schedule of Equity Method Investments [Line Items]      
Number of stores in operation 1,326us-gaap_NumberOfStores    
Equity in earnings (loss) of unconsolidated affiliate $ 16.2us-gaap_IncomeLossFromEquityMethodInvestments $ 17.6us-gaap_IncomeLossFromEquityMethodInvestments $ 17.5us-gaap_IncomeLossFromEquityMethodInvestments
Casa Ley [Member]      
Schedule of Equity Method Investments [Line Items]      
Percentage of ownership in Casa Ley, S.A. de C.V. 49.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= swy_CasaLeyMember
49.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= swy_CasaLeyMember
49.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= swy_CasaLeyMember
Number of stores in operation 206us-gaap_NumberOfStores
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= swy_CasaLeyMember