Employee Benefit Plans (Details) (USD $) In Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2011	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Pension Benefits
Components of net periodic benefit expense
Service cost		$ 10	$ 10	$ 20	$ 18
Interest cost		15	16	32	32
Expected return on plan assets		(19)	(17)	(38)	(35)
Amortization of net actuarial loss		10	8	19	17
Net periodic benefit expense (income)		16	17	33	32
Employee Benefit Plans (Textuals) [Abstract]
Employer contributions under plan	30			33
Additional contributions to plans anticipated for remainder of 2011		5		5
Other Postretirement Benefits
Components of net periodic benefit expense
Service cost				1	1
Interest cost		3	4	7	8
Expected return on plan assets		(2)	(2)	(5)	(5)
Amortization of prior service cost (credit)		(2)	(4)	(5)	(7)
Amortization of net actuarial loss		1	1	2	1
Amortization of regulatory asset			1		1
Net periodic benefit expense (income)		0	0	0	(1)
Employee Benefit Plans (Textuals) [Abstract]
Employer contributions under plan				7
Additional contributions to plans anticipated for remainder of 2011		$ 8		$ 8