Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Property, Plant and Equipment) (Details)

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Summary of Significant Accounting Policies (Property, Plant and Equipment) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Property, Plant and Equipment [Line Items]    
Property and equipment, net $ 326 $ 250
Building    
Property, Plant and Equipment [Line Items]    
Useful life 30 years  
Building And Leasehold Improvements    
Property, Plant and Equipment [Line Items]    
Useful life 20 years  
Software and Software Development Costs    
Property, Plant and Equipment [Line Items]    
Property and equipment, net $ 69 $ 64
Minimum | Furniture, fixtures and equipment    
Property, Plant and Equipment [Line Items]    
Useful life 3 years  
Minimum | Software and Software Development Costs    
Property, Plant and Equipment [Line Items]    
Useful life 3 years  
Maximum | Furniture, fixtures and equipment    
Property, Plant and Equipment [Line Items]    
Useful life 7 years  
Maximum | Software and Software Development Costs    
Property, Plant and Equipment [Line Items]    
Useful life 5 years