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Debt - Additional Information (Detail) - USD ($) | 9 Months Ended |
--- | --- | ---
Sep. 30, 2019 | Dec. 31, 2018
Debt Instrument [Line Items] |  |
Capitalization ratio, Maximum | 60.00% |
Capitalization ratio, Actual | 25.40% |
Outstanding letters of credit under various bilateral letter of credit facilities | $ 456,000,000 |
Unsecured Debt [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Debt Instrument [Line Items] |  |
Fair value of Unsecured Senior Notes | 2,422,000,000 | $ 2,211,000,000
Five Year Unsecured Revolving Credit Facility [Member] |  |
Debt Instrument [Line Items] |  |
Credit facility, borrowing capacity | $ 3,000,000,000.0 |
Credit facility, Period | 5 years |
Credit facility, maturity date | Jun. 27, 2022 |
Credit facility, extendable borrowing capacity | $ 4,000,000,000.0 |
Variable rate basis | LIBOR, NIBOR or CDOR plus |
Interest rate under multi currency facility | LIBOR, NIBOR or CDOR plus 1.125% |
Borrowings under commercial paper | $ 0 |
Outstanding letters of credit issued | 0 |
Funds available under revolving credit facility | $ 3,000,000,000.0 |
Five Year Unsecured Revolving Credit Facility [Member] | Canadian Dollar Offered Rate (CDOR) [Member] |  |
Debt Instrument [Line Items] |  |
Variable rate | 1.125% |

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- Definition Interest rate under multicurrency facility. + References No definition available. + Details
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- Definition Line of credit facility covenant compliance debt to capitalization percentage. + References No definition available. + Details
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- Definition Line of credit facility covenant terms maximum debt to capitalization percentage. + References No definition available. + Details
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- Definition Line of credit facility extended borrowing capacity. + References No definition available. + Details
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- Definition Outstanding letters of credit under various bilateral committed letter of credit facilities. + References No definition available. + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(13)(2)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)(a)(3)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
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- Definition The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR. + References No definition available. + Details
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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. + Details
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- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
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- Definition Date the credit facility terminates, in CCYY-MM-DD format. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Period remaining on line of credit facility before it terminates, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
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