Employee Benefit Plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets contributions by employer	$ 6		$ 15
Total estimated contributions by employer during fiscal year	21		21
Defined Benefit Plan, Expected Future Benefit Payment, Remainder of Fiscal Year	6		6
Postretirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets contributions by employer	0		1
Total estimated contributions by employer during fiscal year	2		2
Defined Benefit Plan, Expected Future Benefit Payment, Remainder of Fiscal Year	1		1
Postemployment Retirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets contributions by employer	4		11
Total estimated contributions by employer during fiscal year	30		30
Defined Benefit Plan, Expected Future Benefit Payment, Remainder of Fiscal Year	19		19
Net benefit cost	$ 20	$ 4	$ 31	$ 22