Debt - Classification and Utilization (Detail) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Debt
Debt maturing or subject to remarketing within twelve months	$ 1,300
Current portion of long-term debt	211	$ 432
4.75% senior notes due June 2020 [Member]
Debt
Debt instrument face amount	$ 600
Interest rate (as a percent)	4.75%
Tax Exempt Bonds [Member]
Debt
Debt with interest rate periods that expire in the next 12 months	$ 529
Current portion of long-term debt	124
Debt maturing or subject to remarketing within twelve months classified as long-term	1,100
Variable-rate tax-exempt bonds	$ 154
Tax Exempt Bonds [Member] \| Minimum [Member]
Debt
Interest rate (as a percent)	1.35%
Tax Exempt Bonds [Member] \| Maximum [Member]
Debt
Interest rate (as a percent)	4.30%
Financing leases and other [Member]
Debt
Current portion of long-term debt	$ 211
Financing leases and other [Member] \| Maximum [Member]
Debt
Interest rate (as a percent)	9.00%
Revolving Credit Facility [Member]
Debt
Outstanding borrowings under credit facility	$ 0
Maximum capacity	2,750
Letters of credit outstanding	412
Unused and available credit capacity	2,300
Commercial Paper Program [Member]
Debt
Commercial paper, borrowings	$ 0
Debt term	397 days
Other Letter of Credit Facilities [Member]
Debt
Letters of credit outstanding	$ 544

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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- Definition

Amount of short-term debt and current maturity of long-term debt and capital lease obligations due within one year or the normal operating cycle, if longer.

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- Definition

Face (par) amount of debt instrument at time of issuance.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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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.

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- Definition

Period of time between issuance and maturity of debt instrument, 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 amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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No definition available.

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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- Definition

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ References

No definition available.

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- Definition

Amount of short-term borrowings, long-term debt and financing leases due or subject to remarketing within the next twelve months, including amounts classified as current and amounts classified as noncurrent due to intent and ability to refinance.

+ References

No definition available.

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- Definition

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- Definition

Represent debt with interest rate periods that expire within the next 12 months.

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