Accounting Policies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]				true
Change in Accounting Principle, Accounting Standards Update, Adoption Date				Jan. 31, 2021
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]				true
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201601Member		us-gaap:AccountingStandardsUpdate201409Member
Expense related to valuation of inventory		$ 20
Accrued freight charges adjustments	$ 8
Prepaid Expenses and Other Current Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted cash				$ 56	$ 72
Other Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted cash				$ 15