Stock-Based Compensation Programs - Compensation expense (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-Based Compensation Programs
Share based compensation expense	$ 40	$ 43	$ 37
Expenses for share-based compensation arrangements, after tax	(35)	$ (37)	$ (33)
Unrecognized compensation cost related to nonvested share-based compensation arrangements	$ 64
Expected weighted-average period for recognition of unrecognized stock-based compensation costs	2 years 4 months 24 days

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Amount, after tax, of expense for award under share-based payment arrangement.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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