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.

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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: 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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: 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(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date the credit facility first became available, in CCYY-MM-DD format.

+ References

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Namespace Prefix:	us-gaap_
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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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Period Type:	duration

- 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

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	instant

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Liquidity Facilities and Letters of Credit - Additional Information (Details) - USD ($)	1 Months Ended
	Nov. 30, 2017	Sep. 30, 2018	Mar. 31, 2018
364 Day Credit Agreement Expiring 2019 [Member]
Line Of Credit Facility [Line Items]
Initiation date	Nov. 30, 2017
Maximum borrowing capacity	$ 5,000,000,000
Credit facilities amount outstanding		$ 0	$ 0
Three Year Agreement Expiring 2021 [Member]
Line Of Credit Facility [Line Items]
Initiation date	Nov. 30, 2017
Maximum borrowing capacity	$ 5,000,000,000
Credit facilities amount outstanding		0	0
Five Year Agreement Expiring 2023 [Member]
Line Of Credit Facility [Line Items]
Initiation date	Nov. 30, 2017
Maximum borrowing capacity	$ 5,000,000,000
Credit facilities amount outstanding		0	0
Total Committed Bank Credit Facilities [Member]
Line Of Credit Facility [Line Items]
Maximum borrowing capacity		5,600,000,000
Committed Bank Credit Facility Expiring 2019 [Member]
Line Of Credit Facility [Line Items]
Maximum borrowing capacity		2,100,000,000
Credit facilities amount outstanding		0	0
Committed Bank Credit Facility Expiring 2020 [Member]
Line Of Credit Facility [Line Items]
Maximum borrowing capacity		825,000,000
Credit facilities amount outstanding		0	0
Committed Bank Credit Facility Expiring 2021 [Member]
Line Of Credit Facility [Line Items]
Maximum borrowing capacity		2,200,000,000
Credit facilities amount outstanding		0	0
Committed Bank Credit Facility Expiring 2022 [Member]
Line Of Credit Facility [Line Items]
Maximum borrowing capacity		475,000,000
Credit facilities amount outstanding		$ 0	$ 0