Business, Basis of Presentation and Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment cost basis	$ 376	$ 373
Total accumulated depreciation	269	261
Depreciation expense	$ 19	$ 25	$ 24
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful lives	3 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful lives	40 years