Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		15 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Income Tax [Line Items]
Payroll tax deferral from CARES Act through December 2020					$ 73
Income taxes	$ 169	$ 165	$ 280	$ 259
Effective income tax rate	23.00%	24.00%	22.00%	23.00%
Unfavorable discrete items, percentage impact	(1.00%)	(1.00%)