Employee Retirement Plans - Schedule of Net Periodic Pension Cost (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Qualified Plan
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	$ 1		$ 1	$ 3	$ 2
Interest cost	1		5	14	18
Expected return on plan assets	(1)		(6)	(8)	(17)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		$ 406		406	0
Amortization of net loss	2		7	13	18
Net periodic pension cost	3		7	428	21
Nonqualified Plan
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	0		0	0	0
Interest cost	2		2	3	4
Expected return on plan assets	0		0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement				0	0
Amortization of net loss	0		0	2	2
Net periodic pension cost	$ 2		$ 2	$ 5	$ 6