Revenue Recognition Contract Assets (Liabilities) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2021	Jun. 30, 2021	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Unbilled receivables (contract assets)	$ 500	$ 500	$ 458
Customer advances (contract liabilities)	(774)	(774)	(583)
Net contract liabilities	(274)	(274)	$ (125)
Revenue recognized, included in beginning contract liability	$ 53	$ 415