Debt (Short Term Debt Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
Short-term debt	$ 11,747,000,000	$ 9,440,000,000
Line of credit | Accounts receivable securitization facility expiring 2019
Short-term Debt [Line Items]
Short-term debt	850,000,000	$ 695,000,000
Average month-end debt outstanding	$ 796,000,000
Weighted-average interest rate on average debt outstanding	2.90%
Maximum month-end debt outstanding	$ 870,000,000
Line of credit facility, maximum borrowing capacity	$ 975,000,000
Extension period	364 days
Collateral amount	$ 1,158,000,000