Property and Equipment, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Gross Amount	$ 777	$ 830
Accumulated Depreciation and Amortization	(524)	(591)
Net Amount	253	239
Depreciation and amortization excluding intangible amortization	82	79	$ 81
Minimum Lease Payments, Sale Leaseback Transactions, Fiscal Year Maturity [Abstract]
Minimum Lease Payments, Sale Leaseback Transactions, Next Twelve Months	5
Minimum Lease Payments, Sale Leaseback Transactions, within Two Years	5
Minimum Lease Payments, Sale Leaseback Transactions, within Three Years	5
Minimum Lease Payments, Sale Leaseback Transactions, within Four Years	5
Minimum Lease Payments, Sale Leaseback Transactions, within Five Years	5
Minimum Lease Payments, Sale Leaseback Transactions, Thereafter	9
Minimum Lease Payments, Sale Leaseback Transactions	34
Future Minimum Sublease Rentals, Sale Leaseback Transactions, Fiscal Year Maturity [Abstract]
Future Minimum Sublease Rentals, Sale Leaseback Transactions, Next Twelve Months	(3)
Future Minimum Sublease Rentals, Sale Leaseback Transactions, within Two Years	(3)
Future Minimum Sublease Rentals, Sale Leaseback Transactions, within Three Years	(3)
Future Minimum Sublease Rentals, Sale Leaseback Transactions, within Four Years	(3)
Future Minimum Sublease Rentals, Sale Leaseback Transactions, within Five Years	(3)
Future Minimum Sublease Rentals, Sale Leaseback Transactions, Thereafter	0
Future Minimum Sublease Rentals, Sale Leaseback Transactions	(15)
Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Gross Amount	403	449
Accumulated Depreciation and Amortization	(289)	(355)
Net Amount	114	94
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Amount	122	119
Accumulated Depreciation and Amortization	(98)	(97)
Net Amount	24	22
Equipment [Member]
Property, Plant and Equipment [Line Items]
Gross Amount	132	133
Accumulated Depreciation and Amortization	(101)	(92)
Net Amount	31	41
Building [Member]
Property, Plant and Equipment [Line Items]
Gross Amount	72	72
Accumulated Depreciation and Amortization	(32)	(30)
Net Amount	40	42
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Gross Amount	7	19
Accumulated Depreciation and Amortization	(4)	(17)
Net Amount	3	2
Land [Member]
Property, Plant and Equipment [Line Items]
Gross Amount	3	3
Accumulated Depreciation and Amortization	0	0
Net Amount	3	3
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Gross Amount	38	35
Accumulated Depreciation and Amortization	0	0
Net Amount	38	35
Capitalized software, balance	22	22
Software Development [Member]
Property, Plant and Equipment [Line Items]
Capitalized internally developed software costs	53	46	42
Depreciation and amortization excluding intangible amortization	$ 36	$ 36	$ 41