Pension Plans and Postretirement Benefits Other Than Pensions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Plans
Pension and Other Postretirement Benefits
Employer contributions	$ 7
Additional plan year contributions	279
Expense components are:
Service cost	43	43
Interest cost	49	52
Expected return on plan assets	(59)	(60)
Amortization of prior service cost (credit)	1	2
Amortization of net loss	18	6
Expense under accounting standards	52	43
Regulatory adjustment (deferred)	25	(6)
Total expense recognized	77	37
Postretirement Benefits Other Than Pensions
Pension and Other Postretirement Benefits
Employer contributions	6
Additional plan year contributions	59
Expense components are:
Service cost	13	11
Interest cost	30	33
Expected return on plan assets	(27)	(28)
Amortization of prior service cost (credit)	(9)	(9)
Amortization of net loss	12	9
Expense under accounting standards	$ 19	$ 16