Sale of Accounts Receivable (Narrative) (Details) $ in Millions, € in Billions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 EUR (€)	Dec. 31, 2017 USD ($)
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Transfer of Financial Assets Accounted for as Sales, Fair Value of Derecognized Assets	$ 2,000		$ 2,000			$ 1,700
Transfer of Financial Assets Accounted for as Sales, Cash Proceeds Received for Assets Derecognized, Amount	1,500		1,500			1,400
Retained Interest, Fair Value Disclosure	475		475			$ 307
Proceeds from Sale of Other Receivables			26,300	$ 24,300
Proceeds from Collection of Retained Interest in Securitized Receivables			8,804	8,493
Loss on transfer of accounts receivables to purchasers	4	$ 2	14	$ 7
Accounts Receivable Securitization Facility [Member]
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,800		1,800
First Purchasers [Member] | Accounts Receivable Securitization Facility [Member]
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,200		1,200
Second Purchasers [Member] | Accounts Receivable Securitization Facility [Member]
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 600		$ 600		€ 0.5