Debt, Description of short-term debt (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Aug. 31, 2015	Dec. 31, 2014
Description of short-term debt [Line Items]
Weighted average interest rate, short-term debt (in hundredths)	0.40%		0.40%
$2,000 million Senior Revolving Credit Facility [Member]
Description of short-term debt [Line Items]
Expiration date	2020-06
Maximum allowed letters of credit	$ 500
Maximum borrowing capacity	$ 2,000		$ 2,000
Terms of debt covenants	The facility contains customary covenants and warranties, including specified restrictions on indebtedness and liens. In addition, we are required to maintain a leverage ratio at the end of every quarter of 3.50 to 1.00 or less for the period covering the most recent four quarters.
Current availability under facility	$ 1,466
Outstanding borrowings	0
Outstanding letters of credit	0
Commercial paper [Member]
Description of short-term debt [Line Items]
Maximum borrowing capacity	2,000
Outstanding borrowings	$ 493
$900 million U.S. Receivables Securitization Facility [Member]
Description of short-term debt [Line Items]
Expiration date	2018-08
Maximum allowed letters of credit	$ 200
Maximum borrowing capacity	900	$ 1,000
Current availability under facility	815
Outstanding borrowings	0
Outstanding letters of credit	0
Additional borrowing capacity, uncommitted loans	$ 300