Debt (Debt) (Details) - USD ($) $ in Millions |
Jun. 30, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | $ 11,841 | $ 11,937 |
| Debt, Current | 197 | 221 |
| Long-term Debt, Excluding Current Maturities | 11,644 | 11,716 |
| Unsecured Debt [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 3,409 | 3,406 |
| Loans Payable [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 2,642 | 3,277 |
| Corporate Debt Securities [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 2,407 | 1,789 |
| Notes Payable, Other Payables [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 1,643 | 1,715 |
| Secured Debt [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 1,559 | 1,565 |
| Capital Lease Obligations [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | $ 181 | $ 185 |