Employee Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Qualified
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	$ 1	$ 0	$ 2	$ 2
Interest cost	13	13	34	36
Expected return on plan assets	(15)	(12)	(34)	(35)
Amortization of net loss	5	5	12	14
Net periodic pension cost	4	6	14	17
Non-Qualified
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	0	0	0	0
Interest cost	1	1	5	5
Expected return on plan assets	0	0	0	0
Amortization of net loss	1	1	2	2
Net periodic pension cost	$ 2	$ 2	$ 7	$ 7