Employee Benefits Schedule of Net Benefit Costs (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 2	$ 2
Interest cost on benefit obligation	3	4	4
Expected return on plan assets	(1)	(1)	(1)
Amortization of prior service cost	1	1	1
Amortization of net actuarial loss	1	1	1
Net periodic benefit cost	6	7	7
Non Qualified Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost on benefit obligation	1	1	1
Expected return on plan assets	0	0	0
Amortization of prior service cost	0	0	0
Amortization of net actuarial loss	1	1	1
Net periodic benefit cost	2	2	2
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	14	12	11
Interest cost on benefit obligation	31	29	28
Expected return on plan assets	(41)	(42)	(39)
Amortization of prior service cost	0	1	1
Amortization of net actuarial loss	17	8	3
Net periodic benefit cost	$ 21	$ 8	$ 4