Employee Benefit Plans Employee Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 2
Interest cost	14	15
Expected return on plan assets	(19)	(19)
Net amortization	12	9
Net periodic benefit cost	8	7
Other Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2
Interest cost	6	7
Expected return on plan assets	(7)	(8)
Net amortization	2	1
Net periodic benefit cost	$ 3	$ 2