Employee Benefit Plans - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
MIP and LTI deferred cash plan - expense	$ 36	$ 28
Fair value of options granted per share	$ 7.83	$ 12.20
Recognized stock-based compensation tax benefit	9	5
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 21.67
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures	754,450
Supplemental Retirement Benefit plans, anticipated employer contributions/benefit payments	28
Supplemental Retirement Benefit plans, actual contributions/benefit payments	1
Contributed To Postretirement Welfare Plan	1
Expected Medicare Subsidy Reimbursement Amount	3
Pension Plans, Defined Benefit
Expected long-term rate of return on plan assets	7.00%
Other Postretirement Benefit Plans, Defined Benefit
Expected long-term rate of return on plan assets	6.25%
Salary Shares [Member]
Amount paid during period in salary shares	$ 4	$ 7
Restricted Stock [Member]
Options granted	1,555,430
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 21.67
Restricted Stock Units (RSUs) [Member]
Options granted	1,581,900
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 20.89

Contributions to Postretirement Plan

No definition available.

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- Definition

Expected Medicare Subsidy Reimbursement Amount

+ References

No definition available.

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- Definition

Amount of expense recognized related to the long-term cash incentive plan

+ References

No definition available.

+ Details

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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (k)(3)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 87

-Paragraph 264

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph j

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Expected Long-Term Rate of Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512013

-Topic 715

-SubTopic 30

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- Definition

The increase in the fair value of plan assets from contributions made by the employer.

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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- Definition

The employer's best estimate, as soon as it can be reasonably determined, of contributions expected to be paid to the plan in the current remaining fiscal period. Estimated contributions may be presented in the aggregate combining (1) contributions required by funding regulations or laws, (2) discretionary contributions, and (3) noncash contributions.

+ References

No definition available.

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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.

+ References

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- Definition

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).

+ References

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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).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(c)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph c(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

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-Paragraph 2

-Subparagraph (c)(2)(iii)(1)

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- Definition

The liabilities paid during the accounting period for equity-based compensation.

+ References

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- Definition

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

+ References

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- Definition

The weighted average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on stock options awarded under the plan during the reporting period.

+ References

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- Definition

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

+ References

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