Equity Incentive Plans- Nonvested awards (Details) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($)
Equity Incentive Plans
Unrecognized compensation	$ 82
Nonqualified stock options
Equity Incentive Plans
Unrecognized compensation	$ 21
Weighted average vesting period	1 year 5 months 26 days
Restricted stock units
Equity Incentive Plans
Unrecognized compensation	$ 33
Weighted average vesting period	1 year 10 months 6 days
Performance stock awards
Equity Incentive Plans
Unrecognized compensation	$ 28
Weighted average vesting period	1 year 5 months 8 days

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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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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