Employee Benefit Plans - Schedule of Pension Plans with a Benefit Obligation in Excess of Plan Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Plans with projected benefit obligation in excess of plan assets
Plans with projected benefit obligation in excess of plan assets, benefit obligation	$ 2,242	$ 2,045
Plans with projected benefit obligation in excess of plan assets, plan assets	1,898	1,749
Plans with accumulated benefit obligation in excess of plan assets
Plans with accumulated benefit obligation in excess of plan assets, benefit obligation	2,229	2,034
Plans with accumulated benefit obligation in excess of plan assets, plan assets	$ 1,889	$ 1,741