Customer Financing (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Customer Financing [Line Items]
Financing Receivable, Individually Evaluated for Impairment	$ 417	$ 422
Impaired Financing Receivable, Recorded Investment	$ 406	$ 411
B Credit Rating [Member]
Customer Financing [Line Items]
Percentage of Credit Default Rates Applied to Customers	22.90%
BB Credit Rating [Member]
Customer Financing [Line Items]
Percentage of Credit Default Rates Applied to Customers	7.40%
BBB Credit Rating [Member]
Customer Financing [Line Items]
Percentage of Credit Default Rates Applied to Customers	0.80%