Employee Benefits Assets and Liabilities associated with Non-qualified benefit plans (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Non-qualified benefit plan trust	$ 36	$ 44
Non-qualified benefit plan liabilities	101	97
Non Qualified Benefit Plans [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	25	24
Other non-qualified benefit plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Non-qualified benefit plan trust	19	25
Non-qualified benefit plan liabilities	$ 76	$ 73