Operating Revenues (Accounts Receivable) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Revenue from External Customer [Line Items]
Total accounts receivable	$ 105	$ 95
Lease receivables
Revenue from External Customer [Line Items]
Total accounts receivable	87	53
Service receivables
Revenue from External Customer [Line Items]
Total accounts receivable	18	41
Other receivables
Revenue from External Customer [Line Items]
Total accounts receivable	$ 0	$ 1