Significant Accounting Policies - Property and Equipment, Net & Computer Software, Net (Details)		12 Months Ended
	Jan. 01, 2017	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)	5 years
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)		3 years
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)		30 years
Furniture, fixtures and other equipment | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)		3 years
Furniture, fixtures and other equipment | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)		7 years
Purchased software | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)		7 years
Software development, to be sold, leased or otherwise marketed | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)		5 years
Software development, to be sold, leased or otherwise marketed | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)		10 years
Internally developed software | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)		5 years
Internally developed software | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)		7 years