Stock-based compensation plans - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 57,000,000	$ 56,000,000	$ 54,000,000
Recognized income tax benefits related to stock-based compensation	30,000,000	22,000,000	20,000,000
Shares under equity incentive compensation plan for future grant	5,307,228	5,619,632
Stock Option Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Stock options exercisable period, maximum	10 years 1 day
Cash realized from exercise of stock options	153,000,000	28,000,000	55,000,000
Tax benefits realized from exercise of stock options	8,000,000	3,000,000	7,000,000
Intrinsic value of stock options exercised	21,000,000	7,000,000	21,000,000
Total grant date fair value of stock options vested	17,000,000	29,000,000	38,000,000
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Unrecognized compensation cost expected to be recognized over a weighted-average period (in years)	1 year 6 months
Unrecognized compensation cost related to non-vested awards	28,000,000
Shares issued	453,908	451,248	423,002
Weighted-average grant date fair value	36,969,000	38,369,000	31,880,000
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost expected to be recognized over a weighted-average period (in years)	1 year 3 months 18 days
Unrecognized compensation cost related to non-vested awards	7,000,000
Shares issued	278,505	242,282	231,037
Weighted-average grant date fair value	22,139,000	20,921,000	17,039,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued	151,014	0	170,405
Common stock authorized for issuance	1,000,000
Common stock issued through employee stock purchase plan	719,900
Cash received from exercise of stock options	$ 10,117,000		$ 8,998,000
Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issuable under deferred compensation plans	38,593	48,136
Shares issued in connection with deferred compensation plans	133,051
Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issuable under deferred compensation plans	18,816	20,084
Shares issued in connection with deferred compensation plans	182,433

Employee service share based compensation cash received from employee stock ownership plan.

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Award Expiration Period

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- Definition

Share based compensation arrangement by share based payment award options vested in period weighted average grant date fair value.

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- Definition

Share based compensation arrangement by share based payment award shares issued.

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- Definition

Share based compensation arrangement by share based payment award stock issued in period weighted average grant date fair value.

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No definition available.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

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- Definition

The maximum number of shares authorized for issuance under the deferred compensation arrangement as of the balance sheet date.

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- Definition

The number of shares issued pursuant to the terms of the deferred compensation plan as of the balance sheet date.

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- Definition

Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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- Definition

As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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- Definition

Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph a

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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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The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

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- Definition

Number of share instruments newly issued under a share-based compensation plan.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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