Employee Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pension Benefits [Member]
Components of net periodic benefit cost
Service cost			$ 1	$ 1
Interest cost	10	10	20	21
Expected return on assets	(11)	(11)	(22)	(23)
Recognized actuarial net (gain) loss	4	2	6	3
Net periodic benefit cost	3	1	5	2
Other Benefits [Member]
Components of net periodic benefit cost
Service cost		1		1
Interest cost	2	2	4	4
Recognized actuarial net (gain) loss	(2)	(1)	(4)	(2)
Net periodic benefit cost		$ 2		$ 3