Store Closures (Details) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) store	Sep. 30, 2017 USD ($) store	Dec. 31, 2017 USD ($) store
Restructuring and Related Cost, Expected Cost
Number of underperforming store closures | store	5	68
Restructuring charges incurred | $	$ 6	$ 211
Forecast
Restructuring and Related Cost, Expected Cost
Number of underperforming store closures | store			70
Additional Restructuring charges expected to be incurred | $			$ 9