Fair Value Measurements, Level 3 Reconciliation (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investments of Certain Benefit Plans [Member]
Reconciliation of beginning and ending balances for fair value measurements developed using significant unobservable inputs
Balance as of beginning of year	$ 11	$ 10	$ 10
Purchases	0	1	0
Transfers in and/or out of Level 3	0	0	0
Balance as of end of year	11	11	10
The amount of total losses included in income attributable to the change in unrealized losses relating to assets still held at end of period	0	0	0
Investments of Certain Benefit Plans [Member] | Operating Expense [Member] | Refining [Member]
Reconciliation of beginning and ending balances for fair value measurements developed using significant unobservable inputs
Total losses included in refining operating expense	0	0	0
Other Investments [Member]
Reconciliation of beginning and ending balances for fair value measurements developed using significant unobservable inputs
Balance as of beginning of year	0	0	0
Purchases	0	21	1
Transfers in and/or out of Level 3	0	0	0
Balance as of end of year	0	0	0
The amount of total losses included in income attributable to the change in unrealized losses relating to assets still held at end of period	0	(21)	(1)
Other Investments [Member] | Operating Expense [Member] | Refining [Member]
Reconciliation of beginning and ending balances for fair value measurements developed using significant unobservable inputs
Total losses included in refining operating expense	$ 0	$ (21)	$ (1)