Compensation Plans - Schedule of Restricted Stock and RSUs Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Restricted Stock Units
Unvested restricted stock and performance restricted stock units activity
Unvested at the beginning of the period (in shares)	1,139	962
Granted (in shares)		844
Vested (in shares)		(419)
Forfeited (in shares)		(248)
Unvested at the end of the period (in shares)		1,139
Weighted Average Grant Date Fair Value
Unvested at the beginning of the period, Weighted Average Grant Date Fair Value (in dollars per share)	$ 33.41	$ 37.39
Granted, Weighted Average Grant Date Fair Value (in dollars per share)		33.57
Vested, Weighted Average Grant Date Fair Value (in dollars per share)		35.10
Forfeited, Weighted Average Grant Date Fair Value (in dollars per share)		35.04
Unvested at the end of the period, Weighted Average Grant Date Fair Value (in dollars per share)		$ 33.41
Forecast
Weighted Average Grant Date Fair Value
Severance and related charges	$ 9

Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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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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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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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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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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-Name Accounting Standards Codification
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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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