Debt (Debt) (Details) - USD ($) $ in Millions |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | $ 10,785 | $ 11,405 |
| Debt, current portion | 637 | 225 |
| Debt, net of current portion | 10,148 | 11,180 |
| Unsecured Debt [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 3,036 | 3,417 |
| Loans Payable [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 2,976 | 2,995 |
| Corporate Debt Securities [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 2,400 | 2,396 |
| Notes Payable, Other Payables [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 1,264 | 1,498 |
| Secured Debt [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 974 | 984 |
| Capital Lease Obligations [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | 105 | 115 |
| Revolving Credit Facility [Member] | ||
| Debt Instrument [Line Items] | ||
| Debt and Capital Lease Obligations | $ 30 | $ 0 |