v3.8.0.1

Debt (Fair Value of Debt) (Details) - USD ($) $ in Millions | Sep. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | $ 11,484 | $ 12,046
Unsecured Debt [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 3,415 | 3,412
Loans Payable [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 3,152 | 3,165
Corporate Debt Securities [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 1,843 | 2,290
Reported Value Measurement [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 11,438 | 11,926
Reported Value Measurement [Member] | Unsecured Debt [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 3,415 | 3,412
Reported Value Measurement [Member] | Loans Payable [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 3,152 | 3,165
Reported Value Measurement [Member] | Corporate Debt Securities [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 1,843 | 2,290
Reported Value Measurement [Member] | Notes Payable, Other Payable excluding Capital Leases [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt | [1] | 1,484 | 1,506
Reported Value Measurement [Member] | Secured Debt [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 1,544 | 1,553
Fair Value, Inputs, Level 2 [Member] | Unsecured Debt [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 3,307 | 3,343
Fair Value, Inputs, Level 2 [Member] | Loans Payable [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 3,202 | 3,244
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 1,905 | 2,349
Fair Value, Inputs, Level 2 [Member] | Secured Debt [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt |  | 1,554 | 1,567
Fair Value, Inputs, Level 3 [Member] | Notes Payable, Other Payable excluding Capital Leases [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Long-term Debt | [1] | $ 1,516 | $ 1,543
[1] | Excludes a lease that is accounted for as a failed sale-leaseback transaction under U.S. GAAP.

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