Overview and Summary of Significant Accounting Policies - Advertising and Internal Use Software and Website Development Costs (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Advertising expense	$ 399	$ 484	$ 438
Capitalized internally developed software and website development costs	314	301
Amortization expense of previously capitalized internally developed software and website development costs	$ 298	$ 262	$ 262
Minimum \| Internal use software and website development costs
Property, Plant and Equipment [Line Items]
Estimated useful lives	1 year
Maximum \| Internal use software and website development costs
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years

Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Additions made to capitalized computer software costs during the period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
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Amount of expense for amortization of capitalized computer software costs.

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-Name Accounting Standards Codification
-Topic 985
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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