Pension and Other Postretirement Benefits (Details 6) (OPEB, USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Actual return on plan assets:
Ending balance	$ 538,000,000	$ 507,000,000
Private equity funds
Actual return on plan assets:
Ending balance	3,000,000	3,000,000
Real estate funds
Actual return on plan assets:
Ending balance	7,000,000	9,000,000
Level 3
Actual return on plan assets:
Ending balance	10,000,000	12,000,000
Level 3 | Private equity funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	3,000,000	4,000,000
Actual return on plan assets:
Unrealized gains (losses)	0	0
Realized gains (losses)	0	0
Purchases, sales and settlements	0	(1,000,000)
Transfers in (out)	0	0
Ending balance	3,000,000	3,000,000
Level 3 | Real estate funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	9,000,000	7,000,000
Actual return on plan assets:
Unrealized gains (losses)	1,000,000	0
Realized gains (losses)	0	2,000,000
Purchases, sales and settlements	0	0
Transfers in (out)	(3,000,000)	0
Ending balance	$ 7,000,000	$ 9,000,000