Employee Retirement Plans - Schedule of Net Periodic Pension Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Qualified Plan
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	$ 1	$ 0	$ 2	$ 1
Interest cost	5	7	13	13
Expected return on plan assets	(3)	(5)	(7)	(11)
Settlement loss	406	0	406	0
Amortization of net loss	5	5	11	11
Net periodic pension cost	414	7	425	14
Nonqualified Plan
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	0	0	0	0
Interest cost	0	1	1	2
Expected return on plan assets	0	0	0	0
Settlement loss	0	0	0	0
Amortization of net loss	1	1	2	2
Net periodic pension cost	$ 1	$ 2	$ 3	$ 4