Employee Retirement Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Qualified [Member]
Net periodic pension cost for defined-benefit pension plans
Service cost	$ 1		$ 3	$ 1
Interest cost	10	11	20	22
Expected return on plan assets	(9)	(8)	(17)	(16)
Amortization of net loss	4	3	7	5
Net periodic pension cost	6	6	13	12
Non-Qualified [Member]
Net periodic pension cost for defined-benefit pension plans
Interest cost	1	2	3	4
Amortization of net loss	1		1
Net periodic pension cost	$ 2	$ 2	$ 4	$ 4