Employee Benefit Plans (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Components of net periodic benefit cost:
Amortization of regulatory liability	$ 8	$ 2	$ 15	$ 5
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	11	10	33	29
Interest cost	12	14	38	42
Expected return on plan assets	(15)	(16)	(45)	(48)
Amortization of prior service cost (credit)	1	0	1	0
Amortization of net actuarial loss	15	13	45	40
Net actuarial loss from settlements	0	2	0	4
Net periodic benefit cost	24	23	72	67
Other Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	1	1	2	2
Interest cost	2	4	8	10
Expected return on plan assets	(3)	(3)	(7)	(7)
Amortization of prior service cost (credit)	(3)	(2)	(7)	(5)
Amortization of net actuarial loss	1	2	4	6
Amortization of regulatory liability	1	0	1	0
Net periodic benefit cost	$ (1)	$ 2	$ 1	$ 6