Operating Revenues (Operating Revenues) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	$ 267	$ 302
Lease revenues
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	218	257
Service revenues
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	$ 49	$ 45