Sale of Accounts Receivable (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2016	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			$ 16,100	$ 20,800
Collections applied to deferred consideration			16,000	20,600
Cash payments received in exchange for the transfer of accounts receivable	$ 1,500		1,500			$ 1,700
Proceeds from transfer of receivables	1,100		1,100			1,200
Deferred receivables consideration	403		403			$ 513
Loss on transfer of accounts receivables to purchasers	1	$ 1	2	$ 2
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	1,500		1,500
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		$ 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		$ 300