Pension and Other Postemployment Benefits (Details 6) (OPEB, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of changes in the fair value of pension investments
Beginning balance		$ 504
Actual return on plan assets:
Ending balance	473	504
Real estate funds
Reconciliation of changes in the fair value of pension investments
Beginning balance		5
Actual return on plan assets:
Ending balance	3	5
Level 3
Reconciliation of changes in the fair value of pension investments
Beginning balance		5
Actual return on plan assets:
Ending balance	3	5
Level 3 | Real estate funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	5		5
Actual return on plan assets:
Transfers in (out)	(2)
Ending balance	$ 3		$ 5