Summary of Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,105	$ 1,054
Less: accumulated depreciation	(709)	(737)
Total	396	317
Depreciation expense	80	71	$ 70
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	19	23
Data processing equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 662	657
Data processing equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Data processing equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Buildings and leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 253	209
Buildings and leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Buildings and leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	40 years
Furniture and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 171	$ 165
Furniture and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Furniture and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	8 years