Employee Benefit Plans - PAC - Employer Contributions (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year		$ 13		$ 13
Employer contributions				10
PAC | Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year		1		1
United States | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year		13		13
Employer contributions				9
Settlement		4	$ 0	4	$ 0
United States | PAC | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year		4		4
Employer contributions				3
Settlement	$ 4	$ 4	$ 0	$ 4	$ 0
Decrease in underfunded status	$ 84