Company Restructuring - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges		$ 200	$ 0	$ 219	$ 27
Employee costs
Restructuring Cost and Reserve [Line Items]
Cumulative amount incurred to date for active programs		255		255
Exit costs
Restructuring Cost and Reserve [Line Items]
Cumulative amount incurred to date for active programs		30		$ 30
Transformative Growth Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges		$ 198
Transformative Growth Plan | Forecast
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges						$ 290
Transformative Growth Plan | Minimum | Forecast
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	$ 40
Transformative Growth Plan | Maximum | Forecast
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	$ 60