Debt (Debt) (Details) - USD ($) $ in Millions |
Dec. 31, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | $ 12,089 | $ 11,282 |
| Debt, current portion | 221 | 199 |
| Debt, net of current portion | 11,868 | 11,083 |
| Unsecured Debt [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 3,450 | 2,800 |
| Loans Payable [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 3,318 | 2,799 |
| Corporate Debt Securities [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 1,809 | 2,075 |
| Notes Payable, Other Payables [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 1,745 | 1,810 |
| Secured Debt [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 1,580 | 1,596 |
| Capital Lease Obligations [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | $ 187 | $ 202 |