Income Taxes Significant Components of Company's Income Tax Provision from Continuing Operations (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Components of Income Tax [Line Items]
Tax expense at Ireland statutory rate					$ 113	$ 132	$ 193
U.S. state income tax, net of federal benefit					8	15	15
Income subject to the U.S. federal tax rate					(92)	(110)	39
Income subject to rates different than the statutory rate					99	38	(201)
Reserve and valuation allowance adjustments		$ 30	$ (76)		(70)	(284)	31
Impact of acquisitions and divestitures					0	0	16
U.S. Tax Reform discrete items					0	0	108
Restructuring and impairment costs					50	(24)	(4)
Income tax provision					$ 108	$ (233)	$ 197
Ireland statutory rate						12.50%	12.50%
Effective Income Tax Rate Reconciliation, Percent					12.00%
Valuation Allowance, Deferred Tax Asset, Increase, Amount	$ 26			$ 56
Unrecognized Tax Benefit Resulting From Tax Audit Resolution					$ 44
IRELAND
Components of Income Tax [Line Items]
Ireland statutory rate					12.50%