Pension and Other Postemployment Benefits (Details 6) (OPEB, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Actual return on plan assets:
Ending balance	$ 518	$ 538
Private equity funds
Actual return on plan assets:
Ending balance	0	3
Real estate funds
Actual return on plan assets:
Ending balance	5	7
Level 3
Actual return on plan assets:
Ending balance	5	10
Level 3 | Private equity funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	3	3
Actual return on plan assets:
Unrealized gains (losses)	(1)	0
Realized gains (losses)	0
Purchases, sales and settlements	0
Transfers in (out)	(2)	0
Ending balance	0	3
Level 3 | Real estate funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	7	9
Actual return on plan assets:
Unrealized gains (losses)	0	1
Realized gains (losses)	0
Purchases, sales and settlements	0
Transfers in (out)	(2)	(3)
Ending balance	$ 5	$ 7