Employee Retirement Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Qualified [Member]
Net periodic pension cost for defined-benefit pension plans
Service cost	$ 2	$ 1
Interest cost	10	11
Expected return on plan assets	(8)	(8)
Amortization of net loss	3	2
Net periodic pension cost	7	6
Non-Qualified [Member]
Net periodic pension cost for defined-benefit pension plans
Interest cost	2	2
Net periodic pension cost	$ 2	$ 2