Debt and Credit Agreements - Activity Related to Long-Term Debt (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Movement, Debt Instruments [Roll Forward]
Beginning balance, current portion	$ 19
Beginning balance, long-term portion	11,790
Beginning balance, total	11,809
Long-term debt issued	2,000	$ 850
Long-term debt repaid	(19)
Reclassifications	0
Discount, premium and other activity	(18)
Ending balance, current portion	18
Ending balance, long-term portion	13,754
Ending balance, total	13,772
Current Portion
Movement, Debt Instruments [Roll Forward]
Beginning balance, current portion	19
Long-term debt issued	0
Long-term debt repaid	(19)
Reclassifications	18
Discount, premium and other activity	0
Ending balance, current portion	18
Long-term Portion
Movement, Debt Instruments [Roll Forward]
Beginning balance, long-term portion	11,790
Long-term debt issued	2,000
Long-term debt repaid	0
Reclassifications	(18)
Discount, premium and other activity	(18)
Ending balance, long-term portion	$ 13,754

Movement, Debt Instruments [Roll Forward]

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- Definition

Reclassification of Debt, Long Term Debt to Short Term Debt

+ References

No definition available.

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- Definition

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

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- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

+ 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 210.9-03.13,16)
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-Name Accounting Standards Codification
-Topic 944
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-Section S99
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Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Amount of long-term debt and capital leases due within one year or the normal operating cycle, if longer.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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- Definition

The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

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-Publisher FASB
-Name Accounting Standards Codification
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