Employee Retirement Plans (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) plan	Sep. 30, 2014 USD ($)
Net periodic pension cost for the company's defined-benefit pension plans
Number of regional multi-employer pension plans in which the entity participates | plan			1
Qualified
Net periodic pension cost for the company's defined-benefit pension plans
Service cost		$ 1	$ 2	$ 3
Interest cost	$ 13	12	36	38
Expected return on plan assets	(12)	(11)	(35)	(35)
Amortization of net loss	5	2	14	8
Net periodic pension cost	6	4	17	14
Non-Qualified
Net periodic pension cost for the company's defined-benefit pension plans
Interest cost	1	2	5	6
Amortization of net loss	1	1	2	1
Net periodic pension cost	$ 2	$ 3	$ 7	$ 7