Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 30, 2019	Dec. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Rent expense		$ 108
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Lease terms	1 year
Lease renewal terms	1 year
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Lease terms	21 years
Lease renewal terms	10 years