Fair Value Measurements (Commercial Aerospace Financing Commitments) (Details) - USD ($) $ in Billions |
Sep. 30, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Commercial Aerospace [Member] | ||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| Financing and other contractual commitments | $ 13.9 | $ 14.4 |