Fair Value Measurements - Nonrecurring (Details) - USD ($) $ in Millions		Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020		Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other intangible assets, net		$ 287				$ 421
Operating lease right-of-use assets		769				867
Property and equipment, net		$ 349				$ 380
Other intangible assets, net [member] | Fair value [member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other intangible assets, net	[1]			$ 0
Operating lease right-of-use assets [member] | Fair value [member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Operating lease right-of-use assets			$ 10	34	[1]
Property and equipment, net [member] | Fair value [member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Property and equipment, net	[1]			$ 4

[1] Amounts were measured at March 31, 2020, except for $10 million of operating lease right-of-use ("ROU") assets, which were remeasured at June 30, 2020. Additionally, certain of these assets were fully impaired at March 31, 2020, June 30, 2020 and September 30, 2020.