Employee Benefit Plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets contributions by employer	$ 4		$ 9
Total estimated contributions by employer during fiscal year	21		21
Defined Benefit Plan, Expected Future Benefit Payment, Remainder of Fiscal Year	12		12
Postretirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets contributions by employer	1		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	3		7
Total estimated contributions by employer during fiscal year	30		30
Defined Benefit Plan, Expected Future Benefit Payment, Remainder of Fiscal Year	23		23
Net Benefit Cost	$ 6	$ 5	$ 11	$ 18