Pension Benefits - Narrative (Details) - Pension Plan $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended
	Jun. 30, 2019 USD ($) participant	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension expense		$ 7	$ 111		$ 14	$ 135
Cash contributions to the plans		$ 4	7		$ 11	13
Percentage threshold of greater of projected benefit obligation or market value of assets (percent)		10.00%			10.00%
United States
Defined Benefit Plan Disclosure [Line Items]
Number of participants elected to receive settlement | participant	1,300
Lump sum payments under settlement	$ 49
Pre-tax settlement expense			105	$ 17		$ 122
Annuity contracts purchased			280
United States | Other income (expense)
Defined Benefit Plan Disclosure [Line Items]
Pre-tax settlement expense			$ 105