Fair Value Measurements - Reconciliation of Changes in Level 3 Balances (Details) (Fair Value, Measurements, Recurring [Member], Level 3 [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 137	$ (108)	$ (138)
Realized/unrealized gains/(losses) [Abstract]
Other income, net (assets and liabilities, net)	(81)	366	(115)
Other comprehensive income/(loss) (assets and liabilities, net)	0	(1)	(3)
Interest income/(expense) (assets and liabilities, net)	0	90	0
Total realized/unrealized gains/(losses) (assets and liabilities, net)	(81)	455	(118)
Purchases, issues, sales and settlements [Abstract]
Purchases (assets and liabilities, net)	0	5	11
Issues (assets and liabilities, net)	0	73	0
Sales (assets and liabilities, net)	0	0	0
Settlements (assets and liabilites, net)	(56)	120	147
Total purchases, issues, sales, settlements (assets and liabilities, net)	(56)	198	158
Transfers into Level 3 (assets and liabilities, net)	0	0	0
Transfers out of Level 3 (assets and liabilities, net)	0	(408)	(10)
Ending balance	0	137	(108)
Unrealized gains/(losses) on instruments still held	0	65	56
Marketable Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair Value Beginning balance	0	1	4
Realized/unrealized gains/(losses) [Abstract]
Other income, net (assets)	0	0	(4)
Other comprehensive income/(loss) (assets)	0	0	0
Interest income/(expense) (assets)	0	0	0
Total realized/unrealized gains/(losses) (assets)	0	0	(4)
Purchases, issues, sales and settlements [Abstract]
Purchases (assets)	0	5	11
Issues (assets)	0	0	0
Sales (assets)	0	0	0
Settlements (assets)	0	0	0
Total purchases, issues, sales, settlements (assets)	0	5	11
Transfers into Level 3 (assets and liabilities, net)	0	0	0
Transfers out of Level 3 (assets and liabilities, net)	0	(6)	(10)
Fair Value Ending balance	0	0	1
Unrealized gains/(losses) on instruments still held	0	0	0
Derivative Financial Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	137	(109)	(168)
Realized/unrealized gains/(losses) [Abstract]
Other income, net (assets and liabilities, net)	(81)	366	(108)
Other comprehensive income/(loss) (assets and liabilities, net)	0	(1)	(5)
Interest income/(expense) (assets and liabilities, net)	0	90	0
Total realized/unrealized gains/(losses) (assets and liabilities, net)	(81)	455	(113)
Purchases, issues, sales and settlements [Abstract]
Purchases (assets and liabilities, net)	0	0	0
Issues (assets and liabilities, net)	0	73	0
Sales (assets and liabilities, net)	0	0	0
Settlements (assets and liabilites, net)	(56)	120	172
Total purchases, issues, sales, settlements (assets and liabilities, net)	(56)	193	172
Transfers into Level 3 (assets and liabilities, net)	0	0	0
Transfers out of Level 3 (assets and liabilities, net)	0	(402)	0
Ending balance	0	137	(109)
Unrealized gains/(losses) on instruments still held	0	65	56
Retained Interest [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance			26
Realized/unrealized gains/(losses) [Abstract]
Other income, net (assets and liabilities, net)			(3)
Other comprehensive income/(loss) (assets and liabilities, net)			2
Interest income/(expense) (assets and liabilities, net)			0
Total realized/unrealized gains/(losses) (assets and liabilities, net)			(1)
Purchases, issues, sales and settlements [Abstract]
Purchases (assets and liabilities, net)			0
Issues (assets and liabilities, net)			0
Sales (assets and liabilities, net)			0
Settlements (assets and liabilites, net)			(25)
Total purchases, issues, sales, settlements (assets and liabilities, net)			(25)
Transfers into Level 3 (assets and liabilities, net)			0
Transfers out of Level 3 (assets and liabilities, net)			0
Ending balance			0
Unrealized gains/(losses) on instruments still held			$ 0