Stock-Based Compensation Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Stock Options outstanding, Beginning balances	990,254
Number of Stock Options, Granted	1,083,665	1,155,566
Number of Stock Options, Forfeited	(348,696)	(165,312)
Number of Stock Options outstanding, Ending balances	1,725,223	990,254
Number of Stock Options, Vested and expected to vest	1,446,606
Number of Stock Options, Exercisable	442,013
Weighted Average Exercise Price, Stock Options outstanding, Beginning balance	$ 24.36
Weighted Average Exercise Price, Stock Options Granted	9.17	$ 24.37
Weighted Average Exercise Price, Stock Options Forfeited	18.39	24.39
Weighted Average Exercise Price, Stock Options outstanding, Ending balance	15.98	$ 24.36
Weighted Average Exercise Price, Stock Options vested and expected to vest	16.97
Weighted Average Exercise Price, Stock Options exercisable	$ 23.13
Weighted Average Contractual Life (years). Stock Options outstanding	4 years 10 months 24 days	6 years
Weighted Average Contractual Life (years), Stock Options vested and expected to vest	4 years 8 months 12 days
Weighted Average Contractual Life (years), Stock Options exercisable	2 years 3 months 18 days
Aggregate Intrinsic Value, Balances	$ 12
Aggregate Intrinsic Value, Options vested and expected to vest	$ 9

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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