Customer Financing (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Customer Financing [Line Items]
Individually evaluated for impairment	$ 77	$ 55
Impaired financing receivables	66	$ 44
Average recorded investment in impaired receivables	$ 46
B Credit Rating [Member]
Customer Financing [Line Items]
Percentage Of Credit Default Rates Applied To Customers	22.60%
BB Credit Rating [Member]
Customer Financing [Line Items]
Percentage Of Credit Default Rates Applied To Customers	4.70%
BBB Credit Rating [Member]
Customer Financing [Line Items]
Percentage Of Credit Default Rates Applied To Customers	0.90%