Stock Compensation Plans and Other Compensation Arrangements (Unaudited) (Details) - USD ($) shares in Millions, $ in Millions	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Rights and Restricted Performance Stock Rights Grant Date Aggregate Fair Value	$ 92	$ 88
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	0.1	0.2
Vesting period	3 years
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	0.3	0.3
Vesting period	3 years
Cash Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Cash Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Cash Units and Cash Performance Units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred Compensation Cash-based Arrangements, Liability, Current and Noncurrent	$ 36	$ 35
Cash Units and Cash Performance Units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred Compensation Cash-based Arrangements, Liability, Current and Noncurrent	$ 199	$ 194

Restricted Stock Rights and Restricted Performance Stock Rights Grant Date Aggregate Fair Value

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- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for deferred compensation arrangements. Represents currently earned compensation under cash arrangements (such as a profit-sharing plan, rabbi trust, and employee contract--excluding equity-based arrangements) that is not actually paid until a later date.

+ References

No definition available.

+ Details

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

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.

+ References

No definition available.

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