Sale of Accounts Receivable (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Proceeds from Sale and Collection of Receivables	$ 8,400	$ 11,200
Collections applied to deferred consideration	8,300	11,000
Cash payments received in exchange for the transfer of accounts receivable	1,400		$ 1,700
Proceeds from transfer of receivables	1,100		1,200
Deferred receivables consideration	292		$ 513
Loss on transfer of accounts receivables to purchasers	1	$ 1
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	1,600
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	1,300
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	$ 300