Fair Value (Narrative) (Details) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 Customer	Sep. 30, 2018 USD ($)	Jun. 30, 2019 Customer
Receivables | Credit Concentration Risk
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Concentration risk percentage		10.00%		10.00%
Number of major customers | Customer		1		0
Redeemable Noncontrolling Interests
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amounts reclassified into equity as a result of the expiration of a put arrangement			$ 200
Subsequent Event | Redeemable Noncontrolling Interests
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amounts reclassified into equity as a result of the expiration of a put arrangement	$ 120