Employee Benefit Plans - PAC (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]
Service cost		$ 2	$ 1	$ 8	$ 5
Interest cost		4	6	14	16
Expected return on plan assets		(5)	(9)	(16)	(25)
Net amortization		0	(1)	(2)	(5)
Net periodic benefit cost (credit)		1	(3)	4	(9)
PAC | Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost		0	0	1	1
Interest cost		1	2	5	7
Expected return on plan assets		(2)	(3)	(6)	(10)
Net amortization		1	0	1	0
Net periodic benefit cost (credit)		0	(1)	1	(2)
United States | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost		7	4	22	11
Interest cost		21	23	59	69
Expected return on plan assets		(32)	(35)	(101)	(105)
Settlement		4	0	4	0
Net amortization		6	8	19	25
Net periodic benefit cost (credit)		6	0	3	0
United States | PAC | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost		0	0	0	0
Interest cost		8	9	22	27
Expected return on plan assets		(12)	(14)	(39)	(42)
Settlement	$ 4	4	0	4	0
Net amortization		5	4	15	13
Net periodic benefit cost (credit)		$ 5	$ (1)	$ 2	$ (2)