Recently Adopted and Recently Issued Accounting Guidance (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets classified in Other noncurrent assets		$ 131	$ 125	$ 320
Stockholders equity	$ 5,569	3,577	4,605		$ 4,908
Income tax expense	367
Retained earnings (accumulated deficit)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders equity	(374)	$ 364	$ 113		(1,264)
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders equity	73				0
Cumulative Effect, Period of Adoption, Adjustment | Retained earnings (accumulated deficit)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders equity	$ 75				$ 367
ASU 2014-09 | Cumulative Effect, Period of Adoption, Adjustment | Retained earnings (accumulated deficit)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders equity				73
ASU 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment				$ 2