Equity-Indexed Compensation Plans - Liability and Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Outstanding (in units)
Outstanding at beginning of period (in units)	6.8	7.3	8.9
Granted (in units)	3.9	1.7	0.9
Vested (in units)	(3.3)	(1.7)	(1.7)
Cancelled or forfeited (in units)	(0.3)	(0.5)	(0.8)
Outstanding at end of period (in units)	7.1	6.8	7.3
Weighted Average Grant Date Fair Value per Unit
Outstanding at beginning of period (in dollars per unit)	$ 22.19	$ 24.68	$ 29.62
Granted (in dollars per unit)	16.17	23.44	23.52
Vested (in dollars per unit)	22.44	32.42	42.12
Modified (in dollars per unit)		2.15	(6.04)
Cancelled or forfeited (in dollars per unit)	23.12	21.99	26.99
Outstanding at end of period (in dollars per unit)	$ 18.67	$ 22.19	$ 24.68
Units issued in connection with the settlement of vested awards, net of tax withholding (in units)	1.4	0.6	0.6
Units withheld for taxes (in units)	0.6	0.2	0.2
Vested awards settled in cash (in units)	1.3	0.9	0.9
Liability Awards
Equity-Indexed Compensation Plans
Accrued liability related to all outstanding LTIP awards and DERs	$ 13	$ 27
Other current liabilities \| Liability Awards
Equity-Indexed Compensation Plans
Short-term accrued liability related to all outstanding LTIP awards and DERs	10	19
Other long-term liabilities and deferred credits \| Liability Awards
Equity-Indexed Compensation Plans
Long-term accrued liability related to all outstanding LTIP awards and DERs	$ 3	$ 8

Share Based Compensation Arrangement By Share Based Payment Award, Shares Vested In Period Settled In Cash

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Grant date fair value of awards modified during the period.

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No definition available.

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- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for stock option plans and other equity-based compensation arrangements payable within one year (or the operating cycle, if longer).

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-Publisher FASB
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Aggregate carrying value as of the balance sheet date of the liabilities for stock option plans and other equity-based compensation arrangements payable after one year (or the operating cycle, if longer).

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Aggregate carrying value as of the balance sheet date of the liabilities for stock option plans and other equity-based compensation arrangements.

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

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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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- 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).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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

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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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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 shares used to settle grantee's tax withholding obligation for award under share-based payment arrangement.

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Number, after forfeiture, of shares or units issued under share-based payment arrangement. Excludes shares or units issued under employee stock ownership plan (ESOP).

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