Employee Benefit Plans (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	$ 39	$ 41	$ 35
Interest cost	55	64	64
Expected return on plan assets	(64)	(77)	(71)
Amortization of prior service cost (credit)	1	1	1
Amortization of net actuarial loss	53	38	35
Net actuarial loss from settlements	5	4	0
Amortization of regulatory asset	0	0	0
Net periodic benefit cost	89	71	64
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Net actuarial gain (loss)	(51)	(220)	(71)
Prior service credit	0	0	0
Amortization of prior service cost (credit)	1	1	1
Amortization of net actuarial loss and loss from settlements	58	42	35
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss)	8	(177)	(35)
Amounts included in accumulated other comprehensive loss:
Prior service cost (credit)	1
Net actuarial loss	60
Other Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	3	2	2
Interest cost	13	15	15
Expected return on plan assets	(9)	(10)	(9)
Amortization of prior service cost (credit)	(7)	(11)	(14)
Amortization of net actuarial loss	8	3	3
Net actuarial loss from settlements	0	0	0
Amortization of regulatory asset	0	1	1
Net periodic benefit cost	8	0	(2)
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Net actuarial gain (loss)	2	(21)	(12)
Prior service credit	2	2	0
Amortization of prior service cost (credit)	(3)	(4)	(5)
Amortization of net actuarial loss and loss from settlements	3	1	1
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss)	4	(22)	(16)
Amounts included in accumulated other comprehensive loss:
Prior service cost (credit)	(3)
Net actuarial loss	3
Amounts included in net regulatory assets associated with our FERC-regulated gas pipelines:
Prior service credit	(5)
Net actuarial loss	$ 6