Revenue Recognition Contract Assets (Liabilities) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Unbilled receivables (contract assets)	$ 409	$ 409	$ 456
Customer advances (contract liabilities)	(613)	(613)	(519)
Net contract liabilities	(204)	(204)	$ (63)
Revenue recognized, included in beginning contract liability	$ 37	$ 363