Retirement Plans and Other Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Contributions
Expected contributions in 2013	$ 0		$ 0
Expected contributions in 2014	89		89
Defined Pension and Other Postretirement Benefit Costs
Amount of pension and other postretirement benefit costs deferred		3	14	9
Amortization of regulatory assets	2		2
Pension Benefits
Net periodic benefit costs and the portion of these costs charged to expense
Service cost - benefits earned during the period	16	14	48	43
Interest cost on benefit obligation	30	31	90	94
Expected return on plan assets	(35)	(33)	(106)	(100)
Amortization of prior service cost			1	1
Amortization of net actuarial loss	11	7	33	19
Net periodic benefit cost	22	19	66	57
Portion of cost charged to expense	12	7	25	22
Contribution to pension plans			65
Other Benefits
Net periodic benefit costs and the portion of these costs charged to expense
Service cost - benefits earned during the period	7	5	20	17
Interest cost on benefit obligation	12	12	35	35
Expected return on plan assets	(12)	(10)	(34)	(31)
Amortization of net actuarial loss	5	4	15	11
Net periodic benefit cost	12	11	36	32
Portion of cost charged to expense	7	4	13	12
Contributions
Expected contributions in 2012	20		20
Expected contributions in 2013	20		20
Expected contributions in 2014	$ 20		$ 20