Employee Benefits Assets and Liabilities associated with Non-qualified benefit plans (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Non-qualified benefit plan trust	$ 32	$ 36
Non-qualified benefit plan liabilities	102	101
Total Non-qualified benefit plan trust assets [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Non-qualified benefit plan trust	32	36
Non-qualified benefit plan liabilities	102	101
Non Qualified Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Non-qualified benefit plan trust	15	17
Non-qualified benefit plan liabilities	25	25
Other non-qualified benefit plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Non-qualified benefit plan trust	17	19
Non-qualified benefit plan liabilities	$ 77	$ 76