Employee Retirement Plans (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) item	Jun. 30, 2014 USD ($)
Net periodic pension cost for the company's defined-benefit pension plans
Number of regional multi-employer pension plans in which the entity participates | item			1
Qualified
Net periodic pension cost for the company's defined-benefit pension plans
Service cost	$ 1	$ 1	$ 2	$ 2
Interest cost	11	13	23	26
Expected return on plan assets	(12)	(12)	(23)	(24)
Amortization of net loss	5	3	9	6
Net periodic pension cost	5	5	11	10
Non-Qualified
Net periodic pension cost for the company's defined-benefit pension plans
Interest cost	3	2	4	4
Amortization of net loss			1
Net periodic pension cost	$ 3	$ 2	$ 5	$ 4