Stock-Based Compensation (Stock Based Compensation Activity) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Balance	807		810
Options outstanding, intrinsic value	$ 22		$ 27
Stock Issued During Period, Value, Restricted Stock Award, Gross	$ 19	$ 25
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	2 years		2 years 3 months
Time-Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Price, Balance	$ 34.83
Weighted Average Grant Price, Granted at fair market value	34.41	$ 25.88
Weighted Average Grant Price, Vested/exercised	36.00
Weighted Average Grant Price, Canceled	32.00
Weighted Average Grant Price, Balance	$ 34.24		$ 34.83
Number of RSUs, Balance	878
Number of RSUs, Granted at fair market value	528
Number of RSUs, Vested/exercised	(367)
Number of RSUs, Canceled	(18)
Number of RSUs, Balance	1,021		878
Performance-Based and Market-Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Price, Balance	$ 34.11
Weighted Average Grant Price, Granted at fair market value	34.41	$ 23.29
Weighted Average Grant Price, Vested/exercised	36.52
Weighted Average Grant Price, Canceled	41.86
Weighted Average Grant Price, Balance	$ 32.67		$ 34.11
Number of RSUs, Balance	923
Number of RSUs, Granted at fair market value	572
Number of RSUs, Vested/exercised	(146)
Number of RSUs, Canceled	(193)
Number of RSUs, Balance	1,156		923
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 34
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 year 11 months
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 30
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 53

Unrecognized cost of unvested share-based compensation awards.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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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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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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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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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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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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Intrinsic value of equity-based compensation awards outstanding. Excludes stock and unit options.

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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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Aggregate value of stock related to Restricted Stock Awards issued during the period.

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