Pension, Savings, and Other Employee Benefits - Schedule of Benefit Obligation and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Change in benefit obligation
Benefit obligation, beginning of year	$ 836	$ 765
Interest cost	24	30	$ 28
Plan amendments	0	0
Actuarial (gain)/loss	70	103
Actual benefits paid	(37)	(38)
Premium paid for annuity purchase	0	(24)
Benefit obligation, end of year	893	836	765
Change in plan assets
Fair value of plan assets, beginning of year	826	731
Actual return on plan assets	103	154
Employer contributions	4	3
Actual benefits paid – settlement payments	(36)	0
Actual benefits paid – other payments	(1)	(38)
Premium paid for annuity purchase	0	(24)
Fair value of plan assets, end of year	896	826	731
Funded (unfunded) status of the plans	3	(10)
Amounts recognized in the Balance Sheets
Other assets	40	27
Other liabilities	(37)	(37)
Net asset (liability) at end of year	3	(10)
Other Benefits
Change in benefit obligation
Benefit obligation, beginning of year	42	35
Interest cost	1	1	1
Plan amendments	0	1
Actuarial (gain)/loss	4	7
Actual benefits paid	(1)	(2)
Premium paid for annuity purchase	0	0
Benefit obligation, end of year	46	42	35
Change in plan assets
Fair value of plan assets, beginning of year	20	18
Actual return on plan assets	3	3
Employer contributions	1	1
Actual benefits paid – settlement payments	(1)	(2)
Actual benefits paid – other payments	0	0
Premium paid for annuity purchase	0	0
Fair value of plan assets, end of year	23	20	$ 18
Funded (unfunded) status of the plans	(23)	(22)
Amounts recognized in the Balance Sheets
Other assets	20	18
Other liabilities	(43)	(40)
Net asset (liability) at end of year	$ (23)	$ (22)