Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) shares in Millions, $ in Millions		3 Months Ended			6 Months Ended
	Jun. 30, 2017 USD ($)	Sep. 08, 2018 USD ($) store_format shares	Feb. 24, 2018 USD ($)	Sep. 09, 2017 USD ($)	Sep. 08, 2018 USD ($) division store_format segment shares	Sep. 09, 2017 USD ($)	Feb. 25, 2018 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Restricted cash		$ 7.9	$ 10.5	$ 11.6	$ 7.9	$ 11.6
LIFO expense (benefit)		3.4		7.9	12.9	23.6
Equity-based compensation expense		12.2		9.3	25.6	18.1
Income tax benefit from compensation expense		3.3		1.9	6.9	3.7
Compensation cost not yet recognized		$ 33.9			$ 33.9
Number of unvested Phantom units | shares		1.4			1.4
Period for recognition of unrecognized compensation cost					10 months 24 days
Income tax benefit		$ 11.9		$ 67.7	$ 14.9	$ 67.3
Effective income tax rate on loss before income taxes		26.80%		16.00%	22.90%	10.70%
Provisional tax benefit as a result of the Tax Act			430.4
Number of divisions | division					13
Number of reportable segments | segment					1
Number of store format | store_format		1			1
Contract liability related to gift cards		$ 43.7	55.6		$ 43.7
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash distribution made					0.0	$ 250.0
Receivables, net		527.9	615.3		527.9
Other expense (income)		(19.2)		$ (11.7)	(60.0)	4.7
Selling and administrative expenses		3,681.4		3,807.2	8,659.0	8,783.3
Decrease in net cash used in investing activities					(88.2)	(754.4)
Increase in cash, cash equivalents, and restricted cash from adoption of new accounting principle					989.0	(645.3)
ASU 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other expense (income)		6.0			14.2
Selling and administrative expenses		6.0			14.2
ASU 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in net cash used in investing activities						1.7
Increase in cash, cash equivalents, and restricted cash from adoption of new accounting principle						$ 1.7
Retained earnings | ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adopting new accounting principle							$ 5.8
Pharmacy
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Receivables, net		$ 205.0	$ 205.5		$ 205.0
Predecessor
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash distribution made	$ 250.0
Additional compensation cost due to plan modification				$ 2.4