SHARE-BASED COMPENSATION - Narrative (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee discount on company stock	10.00%
Maximum employee salary contribution percentage - ESPP	10.00%
Maximum employee contribution amount - ESPP	$ 25,000
Compensation expense related to share-based plans	48,000,000	$ 55,000,000	$ 41,000,000
Share-based compensation not yet recognized	$ 43,000,000
Unrecognized compensation expense, weighted-average period of recognition	2 years
Tax benefit recognized in earnings for share-based compensation arrangements	$ 8,000,000	$ 1,000,000	$ 3,000,000
2014 Omnibus Incentive Plan \| Time-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
2014 Omnibus Incentive Plan \| Performance-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Citizens Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)	1,947,902	1,677,167	1,174,501
Weighted average grant price (in dollars per share)	$ 32.64	$ 36.21	$ 39.54
Awards vested (in shares)	1,384,091	1,518,836	877,111
Weighted average grant price of awards vested (in dollars per share)	$ 38.59	$ 32.21	$ 30.50
Omnibus Incentive Plan And Directors Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant (in shares)	46,236,889
2014 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant (in shares)	5,024,904

The maximum amount that an employee may utilize with respect to the plan on an annual basis.

No definition available.

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- Definition

Amount, after tax, of expense for award under share-based payment arrangement.

+ References

No definition available.

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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
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- Definition

Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

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- Definition

Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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- Definition

Discount rate from fair value on purchase date that participants pay for shares.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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- Definition

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.

+ References

No definition available.

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- Definition

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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