Variable Interest Entity (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended		9 Months Ended
	Jul. 31, 2012	Dec. 01, 2010 BPD Store	Sep. 30, 2012	Sep. 30, 2011
Minnesota Assets [Member]
Variable Interest Entity [Line Items]
Refinery capacity, barrel-per-day		74,000
Number of convenience stores disposed		166
Issued preferred security	$ 45	$ 80	$ 45
Maximum earnout provision payable to the company	0	125
Term of payment of maximum earnout provision payable to the company, years		8 years
Maximum margin support payable to the buyer	0	60
Term of payment of maximum margin support payable to the buyer, years		2 years
Maximum margin support payable to buyer, in USD per year		30
Collection of receivable due from buyer				107
Receivable due from buyer		107
Guarantees with a maximum exposure		11
Deferred gain from sale		89	86
Cash proceeds, dividends on preferred equity interest	12
Cash proceeds, distribution from VIE's offering	40
Cash proceeds, total	132
Income before income taxes			183
Buyer redeemed Preferred Equity interest	80
Maximum exposure to loss			$ 54
Wisconsin [Member]
Variable Interest Entity [Line Items]
Number of convenience stores disposed		6