Commercial Paper and Long-Term Debt (Narrative) (Details) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($) banks	Dec. 31, 2014 USD ($)
Commercial Paper [Member]
Debt Instrument [Line Items]
Short-term Debt, Weighted Average Interest Rate	0.70%
Five Year $3.0 Billion Credit Facility [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	$ 0
Line of Credit, Credit Facility, Maximum Borrowing Capacity	$ 3,000
Number Of Years Of Revolving Bank Credit	5 years
Number of banks that comprise revolving bank credit facility (banks) \| banks	23
Maximum percentage of indebtedness to total net capital bank covenant	55.00%
Five Year $3.0 Billion Credit Facility [Member] \| Minimum [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate During Period	1.20%
Five Year $3.0 Billion Credit Facility [Member] \| Maximum [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate During Period	1.70%
Three Year $2.0 Billion Credit Facility [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	$ 0
Line of Credit, Credit Facility, Maximum Borrowing Capacity	$ 2,000
Number Of Years Of Revolving Bank Credit	3
Number of banks that comprise revolving bank credit facility (banks)	23
Maximum percentage of indebtedness to total net capital bank covenant	55.00%
364 Day $1.0 Billion Credit Facility [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	$ 0
Line of Credit, Credit Facility, Maximum Borrowing Capacity	$ 1,000
Credit Facility, Number of Days	364
Number of banks that comprise revolving bank credit facility (banks)	23
Maximum percentage of indebtedness to total net capital bank covenant	55.00%
364 Day $1.0 Billion Credit Facility [Member] \| Minimum [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate During Period	1.20%
364 Day $1.0 Billion Credit Facility [Member] \| Maximum [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate During Period	1.70%
Three Year $2.0 Billion Credit Facility [Member] [Member] \| Minimum [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate During Period	1.20%
Three Year $2.0 Billion Credit Facility [Member] [Member] \| Maximum [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate During Period	1.70%
Designated as Hedging Instrument [Member] \| Terminated Interest Rate Swaps [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount	$ 5,200
Subsidiaries [Member]
Debt Instrument [Line Items]
Other Long-term Debt	164	$ 150
Other Long-term Debt, Current	$ 47	$ 34

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Credit Facility, Number of Days

+ References

No definition available.

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- Definition

Maximum percentage of indebtedness to total net capital bank covenant

+ References

No definition available.

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- Definition

Number Of Banks That Comprise Revolving Bank Credit Facility

+ References

No definition available.

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- Definition

Number Of Years Of Revolving Bank Credit

+ References

No definition available.

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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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- 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.

+ References

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

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

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

- Definition

The effective interest rate during the reporting period.

+ References

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Balance Type:	na
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

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Balance Type:	credit
Period Type:	instant

- Definition

Including both current and noncurrent portions, carrying amount as of the balance sheet date of other forms of debt not elsewhere specified in the taxonomy with initial maturities beyond one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of the portion of long-term debt not otherwise specified in the taxonomy that is scheduled to be repaid within one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20
-Article 5

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Weighted average interest rate of short-term debt outstanding.

+ References

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Data Type:	num:percentItemType
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- Details

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- Details

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