Employee Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Qualified
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	$ 1	$ 1	$ 2	$ 2
Interest cost	11	8	30	28
Expected return on plan assets	(12)	(12)	(34)	(36)
Amortization of net loss	4	4	14	13
Net periodic pension cost	4	1	12	7
Non-Qualified
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	0	0	0	0
Interest cost	2	1	5	4
Expected return on plan assets	0	0	0	0
Amortization of net loss	1	1	2	2
Net periodic pension cost	$ 3	$ 2	$ 7	$ 6