Long-Term Debt (Long-Term Debt) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term debt, beginning balance	$ 17,863
Payments and Retirements	(1,692)
New Borrowings	1,600
Long-term debt, ending balance	17,771
Long-term debt	17,863	$ 17,771	$ 17,863
Less: Debt Issuance Cost		(188)	(183)
Less: Debt Premium/(Discount)		53	54
Less: Current Portion		(1,060)	(656)
Long-term Debt, Excluding Current Maturities		$ 16,470	16,970
Weighted average interest rate		8.57%
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance	3,511
Payments and Retirements	(41)
New Borrowings	1,600
Long-term debt, ending balance	5,070
Long-term debt	3,511	$ 5,070	3,511
Weighted average interest rate		6.64%
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance	13,495
Payments and Retirements	(1,651)
New Borrowings
Long-term debt, ending balance	11,844
Long-term debt	13,495	$ 11,844	13,495
Weighted average interest rate		9.51%
Secured Subsidiary Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance	107
Long-term debt, ending balance	107
Long-term debt	107	$ 107	107
Weighted average interest rate		8.35%
Unsecured Subsidiary Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance	750
Long-term debt, ending balance	750
Long-term debt	$ 750	$ 750	$ 750
Weighted average interest rate		6.90%

Weighted average interest rate of long-term debt including debt issuance costs, premiums and or discounts.

No definition available.

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ 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

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-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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-Publisher FASB
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-Section S99
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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

Amount, after accumulated amortization, of debt discount (premium).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28567-108399

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-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
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-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

No definition available.

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- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

No definition available.

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