Employee Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Qualified
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	$ 0	$ 0	$ 1	$ 1
Interest cost	13	10	25	21
Expected return on plan assets	(12)	(9)	(24)	(19)
Amortization of net loss	5	3	10	7
Net periodic pension cost	6	4	12	10
Non-Qualified
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	0	0	0	0
Interest cost	2	3	3	4
Expected return on plan assets	0	0	0	0
Amortization of net loss	0	0	1	1
Net periodic pension cost	$ 2	$ 3	$ 4	$ 5