Employee Stock-based Compensation Plans - Employee Purchases and Aggregate Cost (Details) - Employee Stock Puchase Program - USD ($) shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity, Class of Treasury Stock [Line Items]
Employee share purchases (in shares)	0.6	0.5	0.6
Aggregate cost	$ 20	$ 17	$ 15

Aggregate change in value for stock issued during the period as a result of employee stock purchase plan.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration