Property, Equipment, and Capitalized Software, Net - Depreciation and Amortization (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Recorded in depreciation and amortization:
Amortization of capitalized software	$ 33	$ 42	$ 64
Depreciation and amortization of furniture, equipment, building, and improvements	21	36	42
Amortization of intangible assets	18	21	31
Amortization of finance leases	17
Subtotal	89	99	137
Recorded in cost of service revenue:
Amortization of capitalized software and deferred contract costs	0	28	41
Total depreciation and amortization recognized	$ 89	$ 127	$ 178