Duration of performance evaluation for stock units to vest.

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Percentage of performance conditions achieved.

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Length of time after vesting PSUs are required to be held.

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Quarterly value of shares available for purchase under dividend reinvestment and stock purchase plan.

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Value of annual equity awards to non employee directors.

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Value Of Annual Equity Awards To Non Employee Directors, Future Periods

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

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Amount of noncash expense for share-based payment arrangement.

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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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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).

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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.

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Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

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Number of shares authorized for issuance under share-based payment arrangement.

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

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No definition available.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. 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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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Stock Options, Restricted Stock, and Dividend Reinvestment Plans - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jul. 01, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares)	2,610,929
Award vesting period	3 years
Payment deferral period	2 years
Percent of performance condition achieved	100.00%
Value of annual equity awards to non employee directors	$ 85,000	$ 85,000
Total intrinsic value of options exercised	$ 3,000,000	$ 4,000,000	$ 3,000,000
Stock options granted or converted (in shares)	4,182,737	530,787	394,296
Grants in period, weighted average grant date fair value (in dollars per share)	$ 2.13	$ 2.69	$ 3.89
Stock-based compensation expense	$ 32,000,000	$ 22,000,000	$ 23,000,000
Total income tax benefits recognized	$ 8,000,000	6,000,000	6,000,000
Value Of Annual Equity Awards To Non Employee Directors, Future Periods				$ 122,000
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares)	0
Nonvested Restricted Stock Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized	$ 38,000,000
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition	2 years 6 months
Total grant date fair value of shares vested	$ 24,000,000	$ 15,000,000	$ 13,000,000
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized	$ 1,000,000
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition	2 years 7 months 6 days
Employee Stock Option \| Tranche 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	7 years
Employee Stock Option \| Tranche 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Employee Stock Option \| Tranche 3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Employee Stock Option \| Tranche 4
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	20 years
Phantom Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	659,597
Equity Compensation Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for new awards (in shares)	3,115,117
Number of shares available for grant (in shares)	2,311,791
Performance Condition Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Duration of performance evaluation		3 years	3 years
Performance Condition Awards \| PSUs Granted After 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Post vest holding period	2 years
Percent of performance condition achieved	104.20%
Market Condition Award \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	7 years
Dividend Reinvestment Plan \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Quarterly value of shares available for purchase under dividend reinvestment and stock purchase plan	$ 25
Dividend Reinvestment Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Quarterly value of shares available for purchase under dividend reinvestment and stock purchase plan	$ 10,000
Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for new awards (in shares)	10,558,375
Number of shares available for grant (in shares)	5,279,187